Apparatus for RF active compositions used in adhesion, bonding, and coating

ABSTRACT

An RF heating system. In one aspect of the present invention, the RF heating system includes a first elongated electrode connected to a first node within an impedance matching circuit and a second elongated electrode connected to a second node within the impedance matching circuit, wherein (a) a first portion of the first electrode and a first portion of the second electrode are adjacent to and substantially parallel with each other, (b) a second portion of the first electrode is angled in a direction away from the second electrode, (c) a second portion of the second electrode is angled in a direction away from the first electrode, and (d) a stray electromagnetic field is generated in a region above the space between the first portion of the first electrode and the first portion of the second electrode, whereby the generated stray field can be used to heat a composition when the composition is placed in the region.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of application Ser. No.09/482,553, filed Jan. 13, 2000, now U.S. Pat. No. 6,348,679 which is acontinuation-in-part of application Ser. No. 09/404,200, filed Sep. 23,1999, now ABN which is a continuation-in-part of application Ser. No.09/270,505, filed Mar. 17, 1999, now ABN which claims the benefit ofU.S. provisional application Ser. No. 60/078,282, filed Mar. 17, 1998,the contents of each of which are fully incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the use of media containing ioniccompounds and/or nonionic compounds with high dipole moments as a radiofrequency (RF) susceptors in RF activated systems.

2. Related Art

Radio frequency (RF) heating is a well established non-contact precisionheating method that is used to generate heat directly within RFsusceptors, and indirectly within materials that are in thermallyconductive contact with RF susceptors. RF susceptors are materials thathave the ability to couple and convert RF energy into heat energy withinthe material.

Conventional adhesives are not suitable RF susceptors that can bedirectly heated and activated by RF heating. Rather, these conventionaladhesives are typically heated indirectly through thermally conductivecontact with an RF susceptor material. FIG. 1 illustrates twoconventional methods that are currently used in industry for indirect RFheating of conventional adhesives: The first method is illustrated inFIG. 1A, where susceptor material 102 exists as a bulk macroscopiclayer. RF susceptor material 102 is directly heated by RF energy, andadhesive layer 104 is indirectly heated through thermally conductivecontact with RF susceptor material 102. For example, adhesive layer 104may be applied to a continuous surface of susceptor material 102, suchas steel or aluminum. The second method is illustrated in FIG. 1B, wheresusceptor material 112 consists of discrete macroscopic particles.Adhesive layer 114 is loaded with macroscopic particles of a RFsusceptor material 112, such as macroscopic particles or flakes of metaloxides, metallic alloys, or aluminum. With this conventional method,each RF susceptor particle 112 acts as a discrete RF susceptor,generating heat throughout adhesive layer 114.

An example of a conventional RF energy activated composition, such asthat shown in FIG. 1B, is described in U.S. Pat. No. 5,378,879, issuedto Monovoukas (“Monovoukas”). Monovoukas utilizes macroscopic “loadingparticles” as discrete RF susceptors.. The particles are heated by RFenergy and in turn conduct heat to the surroundings. These macroscopicloading particles are thin flakes (i.e. in thin disk-like configuration)that are designed to be admixed to relatively thick extruded materials.However, these flakes are not well suited for use as susceptors in thinfilm bonding applications in which physical distortions, discolorationsin the surface, or opacity of the bonded films would result from theflakes.

Another example of a conventional inductively activated adhesive isdescribed in U.S. Pat. No. 3,574,031, issued to Heller et al.(“Heller”). Heller describes a method of heat welding thermoplasticbodies using an adhesive layer that contains uniformly dispersedmacroscopic RF susceptors, typically iron oxide particles. Thesediscrete RF susceptor particles are ferromagnetic in nature. Adisadvantage of this type of method is that a tradeoff must be madebetween the size of the particle employed versus the power level andduration of the inductive heating process. For example, if susceptorparticles are kept small in size, the mechanical strength of the bondtends to increase. However, as the size of these discrete susceptors isreduced, the power levels and dwell times required to heat the RFsusceptor material and achieve acceptable bonds tend to increase.Another disadvantage of this type of method is the high levels ofloading of the medium with RF susceptor particles that is required forefficient activation. Such high loading levels detract from the physicalproperties and rheology of the adhesive composition. Still anotherdisadvantage is the dark color and opacity of the composition, whichrenders the composition undesirable for many applications.

An example of adhesive activated by a dielectric process is described inU.S. Pat. No. 5,661,201, issued to Degrand (“Degrand”). Degranddescribes a thermoplastic film including at least one ethylene copolymerand a sufficient quantity of N,N-ethylene-bisstearamide that is capableof being sealed utilizing a current at a frequency of about 27.12megahertz (MHz). A disadvantage of this type of film and sealing processis the inherent tendency to also heat the adherand.

U.S. Pat. No. 5,182,134, issued to Sato, discloses methods of curing athermoset composition by applying-an RF signal having a frequency ofabout 1 to 100 MHz to a composition comprising a major portion of athermoset and a receptor. The receptor is described as being one of thealkali or alkaline earth metal sulfate salts (e.g. calcium sulfate),aluminum trihydrate, quaternary ammonium salts, phosphonate compounds,phosphate compounds, polystyrene sulfonate sodium salts or mixturesthereof. According to this patent, all of the exemplified compositionstook longer than one second to heat.

U.S. Pat. No. 5,328,539, issued to Sato, discloses methods of heatingthermoplastic susceptor compositions by applying an RF signal having afrequency of about 1 to 100 MHz. The susceptors are described as beingone of the alkali or alkaline earth metal sulfate salts (e.g. calciumsulfate), aluminum trihydrate. quaternary ammonium salts, phosphonatecompounds, phosphate compounds. polystyrene sulfonate sodium salts ormixtures thereof. According to this patent, all of the exemplifiedcompositions took longer than one second to heat.

U.S. Pat. No. 4,360,607, issued to Thorsrud, discloses a compositionsuitable for sensitizing thermoplastic compositions to the heatingeffects of microwave energy comprising (1) an alcohol amineor-derivative thereof , (2) a simple or polymeric alkylene glycol orderivative-thereof, (3) silica and, optionally. (4) a plasticizer.

U.S. Pat. No. 5,098,962, issued to Bozich, discloses a water dispersiblehot melt adhesive composition comprising:

(a) from about 40% to 95% by weight of a water dispersible ionicallysubstituted polyester resin having a molecular weight from about 10,000to about 20,000 daltons;

(b) from about 60% to about 5% by weight of one or more compatibleplasticizers; and

(c) from about 0.1% to about 1.5% of one or more compatible stabilizersof the anti-oxidant type.

Examples of plasticizers that may be used according to this patentinclude one or more low molecular weight polyethylene glycols, one ormore low molecular weight glycol ethers, glycerin, butyl benzylphthalate and mixtures thereof.

U.S. Pat. No. 5,750,605, issued to Blumenthal et al., discloses a hotmelt adhesive composition-comprising:

(i) 10 to 90% by weight of a sulfonated polyester condensation polymer;

(ii) 0 to 80% by weight of a compatible tackifier;

(iii) 0 to 40% by weight of a compatible plasticizer;

(iv) 5 to 40% by weight of a compatible wax diluent with a molecularweight below 500 g/mole containing at least one polar functional group,said group being present at a concentration greater than 3×10⁻³equivalents per gram;

(v) 0 to 60% by weight of a compatible crystalline thermoplasticpolymer; and

(vi) 0 to 3% by weight of a stabilizer.

What is needed is a composition (e.g. adhesive composition or coating)containing either dissolved or finely dispersed susceptor constituentsthat are preferably colorless or of low color. Further, the compositionshould be transparent or translucent throughout an adhesive matrix orplastic layer. This type of RF susceptor will result in more direct anduniform heating throughout an adhesive matrix or plastic layer. Further,it is desirable that such a composition will allow bonding with nophysical distortion or discoloration in the bonded region of thin films.Still another desirable feature is activation of the RF susceptors atfrequencies, e.g. of about 15 MHz or below, most preferably about 13.5MHz, which are more economical to generate than higher frequencies anddo not substantially heat dielectric substrates. A further desirablefeature is that the composition can be activated or melted in less thanone second and that it exhibit acceptable shear strength. It is alsodesirable to have a formulation which may be optimized for a particularapplication, such as cutting, coating, or bonding substrates.

SUMMARY OF THE INVENTION

The present invention generally relates to the creation and use of acomposition (also referred to as a “susceptor composition”) that canbond two or more layers or substrates to one another and that can beused to coat or cut a substrate. The susceptor composition is activatedin the presence of radio frequency (RF) energy.

In one embodiment, the susceptor composition of the present inventioncomprises a susceptor and a carrier. The carrier and susceptor areblended with one another and form a mixture, preferably a substantiallyuniform mixture. The susceptor is present in an amount effective toallow the susceptor composition to be heated by RF energy. In apreferred embodiment, the susceptor also functions as an adhesive orcoating.

In another embodiment of the present invention, the susceptorcomposition further comprises an adhesive compound. The adhesivecompound, susceptor, and carrier are blended with one another to form amixture that is activated in the presence of RF energy. Preferably, themixture is substantially uniform.

In another embodiment of the present invention, the susceptorcomposition further comprises at least one of a thermoplastic polymer,thermoset resin, elastomer, plasticizer, filler or other material. Theadditive, susceptor, and carrier are blended with one another to form amixture that is activated in the presence of RF energy.

In yet another embodiment of the present invention, the composition canfurther comprise a second carrier that is an insoluble porous carrierthat is saturated with the composition.

The susceptor is an ionic or polar compound and acts as either acharge-carrying or an oscillating/vibrating component of the susceptorcomposition. The susceptor generates thermal energy in the presence ofan RF electromagnetic or electrical field (hereafter RF field).According to the present invention, the susceptor can be an inorganicsalt (or its respective hydrate), such as stannous chloride (SnCl₂),zinc chloride (ZnCl₂) or other zinc salt, or lithium perchlorate(LiClO₄), or an organic salt, such as lithium acetate (LiC₂H₃O₂). Thesusceptor can be a non-ferromagnetic ionic salt. The susceptor can alsobe a polymeric ionic compound (“ionomer”) which preferably alsofunctions as an adhesive or coating. Under RF power levels of about 0.05kilowatt (kW) to 1 kW, and frequencies of about 1 to 100 MHz, thesusceptor composition of the present invention facilitates (a) thebonding of single layers of polymeric materials such as polyolefins,non-polyolefins, and non-polymeric materials, as well as multilayerstacks of these materials, and (b) coating on a substrate such as aprinted pattern on plastic films, metallic foils, etc.

Surprisingly, it has been discovered that when an ionomer is combinedwith a polar carrier, much more heating occurs when exposed to RF energythan when the ionomer or carrier is exposed separately to RF energy.Also surprisingly, it has been discovered that when the polar carrier ispresent at about 13-30% weight percent, more preferably, about 15-25weight percent, most preferably, about 20-23 weight percent, very shortheating times are possible while retaining acceptable shear strength ofthe bond.

According to another embodiment of the present invention, a method ofbonding a first material or substrate to a second material or substratecomprises interposing a composition according to the invention betweenthe first and second materials and applying RF energy to the compositionto heat the composition, thereby causing the first and second materialsto become bonded. In one embodiment, the composition comprises asusceptor and a carrier that are distributed in one another to form amixture, preferably, a substantially uniform mixture. Optionally, thecomposition may further comprise other compounds and additives asdescribed herein. The susceptor is present in the composition in anamount effective to allow the composition to be heated by RF energy.

According to another embodiment of the present invention, a method ofbonding or adhering a first substrate to a second substrate includes:applying a first composition onto the first substrate; applying a secondcomposition onto the second substrate; contacting the first compositionwith the second composition; applying RF energy to the first and secondcompositions to heat the compositions, thereby causing the first andsecond substrates to become adhered or bonded; wherein one of thecompositions comprises a susceptor and the other of the susceptors is apolar carrier, and the susceptor and/or the carrier are present inamounts effective to allow the first and second compositions to beheated by RF energy.

According to yet another embodiment of the present invention, a methodof bonding or adhering a first substrate to a second substrate includes:applying a first composition onto the first substrate; applying a secondcomposition onto the first composition; contacting the second substratewith the second composition; and applying RF energy to the first andsecond compositions to heat the compositions, thereby causing the firstand second substrates to become adhered or bonded, wherein one of thecompositions comprises a susceptor and the other of the compositions isa polar carrier, and the susceptor and/or the carrier are present inamounts effective to allow the first and second compositions to beheated by RF energy.

According to another embodiment of the present invention, a method ofmaking a susceptor composition comprises admixing a susceptor and acarrier, wherein, preferably, the carrier and susceptor aresubstantially uniformly dispersed in one another and form a uniformmixture. The susceptor and/or carrier are present in the composition inan amount effective to allow the susceptor composition to be heated byRF energy.

According to a further embodiment of the present invention, an adheredor a bonded composition can be obtained according to the disclosedmethods.

According to a further embodiment of the present invention, a kit forbonding a first material to a second material comprises one or morecontainers, wherein a first container contains a composition comprisinga susceptor and a carrier that are dispersed in one another and form amixture. The kit may also contain an adhesive or elastomeric compound orother additives as disclosed herein. The susceptor and/or carrier arepresent in an amount effective to allow the composition to be heated byradio frequency energy.

According to a further embodiment of the present invention, a kit foradhering or bonding a first substrate to a second substrate, comprisesat least two containers, wherein one of the containers comprises asusceptor and another of the containers comprises a polar carrier,wherein when the susceptor and the carrier are applied to substrates andthe susceptor and carrier are interfaced, a composition is formed thatis heatable by RF energy.

The invention also relates to a composition comprising an ionomericpolymer and a polar carrier.

The invention also relates to a method of curing a thermoset resin,comprising combining the thermoset resin with a polar carrier to give amixture and exposing the mixture to RF energy.

The invention relates to an apparatus, having: a first portion having afirst mating surface; a second portion, having a second mating surface;a composition disposed between the first mating surface and the secondmating surface, wherein the composition comprises a susceptor and apolar carrier wherein the susceptor and/or the polar carrier are presentin amounts effective to allow the composition to be heated by RF energy,and wherein the composition adheres the first mating surface to thesecond mating surface such that application of a force to separate thefirst mating surface and the second mating surface results in breakageof the apparatus unless the composition is in a melted state.

The invention also relates to a method of applying a protective film orprinted image/ink on a substrate.

The invention also relates to a method for dynamically bonding a firstadherand to a second adherand. The method includes: (1) creating anarticle of manufacture comprising the first adherand, the secondadherand, and a composition, the composition being between the firstadherand and the second adherand, wherein the composition can beactivated in the presence of an RP field; (2) moving the article ofmanufacture along a predetermined path; (3) generating along a portion,of the predetermined path an RF field having sufficient energy toactivate the composition, wherein the composition is activated by itsless than one second exposure to the RF field.

The invention also relates to a method for applying a susceptorcomposition to a substrate. In one embodiment, the method includes: (1)formulating the susceptor composition as a liquid dispersion; (2)applying the liquid dispersion of the susceptor composition to thesubstrate; (3) drying the susceptor composition, wherein the drying stepincludes the step of applying RF energy across the composition, therebygenerating heat within the liquid dispersion. In a preferred embodiment,one may roll up the substrate after the susceptor composition has dried.

The invention also relates to a method for cutting a substrate. Themethod includes: (1) applying a composition to a portion of thesubstrate, wherein the composition comprises a susceptor and polarcarrier wherein the susceptor and/or said polar carrier are present inamounts effective to allow the composition to be heated by RF energy,and wherein the portion of the substrate defines a first section of thesubstrate and a second section of the substrate; (2) melting the portionof the substrate by heating the composition via RF energy; and (3) afterthe portion of the substrate has begun to melt, applying a force to thesubstrate to separate the first section from the second section.

The method also relates to a method of dynamically bonding a firstsubstrate to a second substrate. The method including: applying acomposition onto the first substrate; after applying the compositiononto the first substrate, forming a roll of the first substrate; storingthe roll; unrolling the roll; and while unrolling the roll; joining anunrolled portion of the first substrate with a portion of the secondsubstrate such that the portion of the second substrate is in contactwith a portion of the composition applied onto the first substrate; andapplying RF energy to the portion of the composition, wherein theportion of the composition heats and melts as a result of the RF energybeing applied thereto.

Further features and advantages of the present invention, as well as thestructure and operation of various embodiments of the present invention,are described in detail below with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIGS. 1A and 1B illustrate conventional schemes for inductively heatingadhesives.

FIG. 2 shows an RF active composition according to the presentinvention.

FIG. 3 shows a susceptor composition placed between two polyolefinlayers to be attached according to the present invention.

FIG. 4 illustrates a block diagram of an RF heating system according toa first embodiment.

FIG. 5 illustrates a block diagram of a heating system according to asecond embodiment.

FIG. 6 illustrates a two probe heating system.

FIGS. 7A and 7B further illustrate the two probe heating system.

FIG. 7C illustrates a probe having a curled end to reduce coronaeffects.

FIG. 8 illustrates one embodiment of an alternating voltage supply.

FIG. 9 is a flow chart illustrating a process for heating a compositionaccording to the present invention.

FIG. 10A further illustrates one embodiment of an impedance matchingcircuit.

FIG. 10B further illustrates another embodiment of an impedance matchingcircuit.

FIG. 11 shows a method of bonding adherents using a composition that isactivated in the presence of RF energy.

FIGS. 12 to 17 illustrate additional embodiments of probes 602 and 604.

FIG. 18 illustrates one embodiment of an application system for applyinga composition according to the present invention to a substrate.

FIG. 19 illustrates one embodiment of a system for bonding or adheringvarious adherents.

FIGS. 20A and 20B illustrates a static bonding: system for bondingadherents.

FIG. 20C illustrates an electrically insulating block for housingprobes.

FIG. 21 illustrates an in-line bonding system.

FIG. 22 further illustrates one embodiment of the in-line bonding systemillustrated in FIG. 21.

FIGS. 23-27 illustrate alternative designs of the in-line bonding systemillustrated in FIG. 21.

FIGS. 28A and 28B illustrate one embodiment of a system for themanufacture of flexible packaging material.

FIG. 29 further illustrates film 2815.

FIG. 30 illustrates one embodiment of film 2870.

FIG. 31 illustrates an alternative system for manufacturing an RFactivated adhesive film for use in the flexible packaging industry.

FIG. 32 illustrates a conventional aseptic package materialconstruction.

FIG. 33 illustrates an aseptic package material according to oneembodiment that does not include metallic foil.

FIG. 34 illustrates another embodiment of an aseptic packaging materialconstruction that does not use metallic foils.

FIG. 35 illustrates a conventional cap sealing construction.

FIG. 36 illustrates a seal, according to one embodiment, for sealing abottle.

FIG. 37 illustrates a design for adhering a flexible bag to an outerbox.

FIG. 38 illustrates a step and repeat manufacturing system.

FIG. 39 illustrates an index table bonding system.

FIG. 40 shows an example experimental set-up utilized to testcompositions according to the present invention.

FIG. 41 illustrates another experimental set-up for testing compositionsaccording to the present invention.

FIG. 42 illustrates test probes.

FIG. 43 illustrates a process for assembling a book, magazine, orperiodical, or the like.

FIG. 44 illustrates a paper substrate coated with a susceptorcomposition.

FIG. 45 illustrates a stack of coated paper substrates.

FIGS. 46 and 47 illustrates one embodiment of an envelope or maileraccording to the present invention.

FIG. 48 illustrates a cross-section of a container sealed with asusceptor composition of the present invention.

FIG. 49 illustrates another example of a device sealed or otherwisejoined together with a composition of the present invention.

FIG. 50 shows another example of a device sealed or otherwise joinedtogether with a composition of the present invention.

FIG. 51 illustrates still another example of a cross-section of acontainer 5100 that has been sealed with the adhesive of the presentinvention.

FIG. 52 illustrates a system for bonding two substrates.

FIG. 53 illustrates another embodiment of a system for bonding twosubstrates.

FIG. 54 depicts a graph showing RF activation time vs. % Glycerin for acomposition comprising AQ55S.

FIG. 55 depicts a graph showing shear holding time vs. % glycerin for acomposition comprising AQ55S.

FIG. 56 depicts a graph showing RF activation time vs. % glycerin for acomposition comprising AQ35S.

FIG. 57 depicts a graph showing shear holding time vs. % glycerin for acomposition comprising AQ35S.

FIG. 58 depicts a family of curves showing RF activation time vs. %various polar carriers.

FIG. 59 depicts a graph showing RF activation time vs. % PARICIN 220 ina composition comprising 80% AQ55S/20% glycerin.

FIG. 60 depicts a graph showing brookfield viscosity vs. % PARICIN 220in a composition comprising 80% AQ55S/20% glycerin.

FIG. 61 depicts a graph showing RF activation time vs. % glycerin in acomposition comprising the sodium salt of an ethylene acrylic acidcopolymer (MICHEM Prime 48525P).

FIG. 62 illustrates a seam sealing system according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Overview and Discussion of the Invention

II. Terminology

A. Sulfonated Polymers

B. Acrylic Acid and Maleic Anhydride Polymers and Copolymers

C. Starch/Polysaccharide Derivatives

D. Proteins

E. Others

III. The Polar Carrier

IV. Further Additives to the Susceptor Compositions

A. Adhesive/Thermoplastic Additives

B. Adhesive/Coating Thermoset Additives

C Surfactant Additives

D. Plasticizer Additives

E. Tackifiers

F. Fillers

G. Stabilizers and Antioxidants

H. Other Additives

V. Applying the Susceptor Compositions to Substrates

VI. Apparatus For Activating the Various Compositions of the PresentInvention

VII. Method of Bonding Substrates

VIII. Additional Probe Embodiments

IX. Applicator System for Applying a Composition of the PresentInvention to a Substrate/Adherand

X. Systems for Adhering or Bonding two Adherands.

XI. Exemplary Specific Applications of the Present Invention

A. Manufacture of Flexible Packaging

B. Food Packaging and Cap Sealing

C. Printing Applications

D. Bookbinding and Mailers

E. Security Devices

F. Thermal Destruction

G. Seam Sealing

XII. Kits

XIII. Experimental Set-up

XIV. Examples

I. Overview and Discussion of the Invention

The present invention is directed towards an RF susceptor compositionand methods and systems of bonding, cutting, and/or coating substratesand surfaces using the susceptor composition. The susceptor compositionis a mixture of RF susceptors and/or adhesive/coating compounds and/orother additives dissolved or finely dispersed in a matrix. Preferably,the RF susceptors and/or adhesive compounds and/or other additives areuniformly dissolved or finely dispersed in the matrix. The susceptorcomposition is capable of coupling efficiently in an RF field having afrequency of about 15 MHz or below. In order to be useful in industryand commercial products, a susceptor composition preferably has thefollowing characteristics: (1) an activation time in the presence of alow power RF field on the order of 1 second or less, (2) adequate bondor adhesive strength for the intended use, (3) transparency ortranslucency and only slight coloration (if any), (4) minimal distortionof the substrates being attached, and (5) on demand bonding ofpreapplied adhesive. Further, it is desirable that the susceptorcomposition have coupling ability in the absence of volatile solvents,although the presence of nonvolatile liquids (such as plasticizers) maybe desirable. These characteristics are important in providingsufficient heat transfer to the substrates or layers to be bonded to oneanother, or for adhesion to take place at the interface. Additionally,the susceptor composition should not interfere with the thermal bondingor inherent adhesive properties of the substrates or layers to be bondedor adhered to one another.

According to the present invention, a susceptor composition used to bondor adhere substrates or layers can be directly heated by exposure to anRF field having frequencies ranging from 1-100 MHz. The susceptorcomposition comprises a susceptor, and a carrier blended with oneanother to form a mixture. In addition, the susceptor composition canfurther comprise one or more adhesive compounds blended with thesusceptor and carrier to form the mixture.

Susceptors are either ionic or polar compounds introduced as a componentof a composition, such that RF heating of the resulting susceptorcomposition occurs. An ionic susceptor is an ionic compound introducedas a sufficiently charge-carrying or oscillating component of thecomposition. A polar susceptor is a polar compound which hassufficiently high dipole moment that molecular oscillations orvibrations of the compound occur when exposed to an RF field. As shownin FIG. 2, a susceptor composition 202 comprises a continuous mixture ofsusceptors such as microscopic, ionic salts or polymeric ionic compoundsor dipoles 204, which generate thermal energy in the presence of the RFfield. It has been discovered that acceptable bonding results occur withinorganic salts such as stannous chloride (SnCl₂); zinc salts such aschloride (ZnCl₂), bromide (ZnBr₂) and the like; and lithium perchlorate(LiClO₄), and organic salts such as lithium acetate (LiC₂H₃O₂). Thesesalts or combination of salts, when distributed in the mixture, createan ionic and/or polar medium capable of being heated by RF energy.

II. Terminology

“RF Energy” means an alternating electromagnetic field having afrequency within the radio frequency spectrum.

A “susceptor composition” comprises a susceptor and a carrier interfacedwith one another and/or mixed or blended together. Preferably, thesusceptor and carrier are mixed together. More preferably, the susceptorand carrier are substantially uniformly mixed together. In anotherembodiment, the susceptor and carrier are interfaced together bydisposing a layer of the susceptor onto a layer of the carrier or visaversa. In this embodiment, the susceptor may be coated onto a firstsubstrate and the carrier, with or without added ingredients such as awax or other additives that prevent the carrier from evaporatingsubstantially, may be coated onto a second substrate. The first andsecond substrates containing the susceptor and carrier layers,respectively, may then be brought into contact or interfaced andactivated then or at a later time.

The susceptor compositions of the invention may further comprise one ormore adhesive compounds or other additives mixed, preferablysubstantially uniformly mixed, together with the susceptor and thecarrier. The susceptor composition is activated in the presence of radiofrequency (RF) energy. The susceptor composition can be used to bond twoor more layers or substrates to one another, can be used as a coating,and can be used to thermally cut substrates.

A “carrier” provides the mobile medium in which the susceptors aredissolved, distributed, or dispersed. Preferably, the carrier is a polarcarrier as defined below which enhances the activation of thecompositions. Carriers (also referred to as mobile media) can beliquids, such as solvents and plastisizers, or polymers that areutilized for their polar functionality and for their ability to beheated by RF energy.

An “adhesive compound” refers to polymers, copolymers and/or ionomers asdescribed herein that are blended into the susceptor composition toenhance its adhesive properties.

“Bonding” is defined as the joining of one substrate to anothersubstrate to cause a physical joining process to occur.

“Adhesion” is an interaction between two adherands at their interfacesuch that they become attached or joined.

A “substantially transparent” mixture refers to a mixture that transmitsgreater than about 50% of incident visible light.

“Thermal bonding” or “welding” is defined as the reflowing of onesubstrate into another substrate to cause a physical joining process tooccur.

“Mechanical bonding” occurs between adherands when a susceptorcomposition holds the adherands together by a mechanical interlockingaction.

An RF “susceptor” converts coupled RF energy into heat energy in thesusceptor composition. According to the present invention, thesusceptor, as described above, is either the charge carrying oroscillating ionic compound or the oscillating polar compound having asufficiently high dipole moment comprising a composition to generatethermal energy in the presence of an RF field. Generally, the susceptorcan be a salt. For example, the susceptor can be an inorganic salt orits respective hydrate(s), such as stannous chloride (SnCl₂). stannouschloride dihydrate (SnCl₂x2H₂O), lithium perchlorate (LiClO₄), lithiumperchlorate trihydrate (LiCO₄x3H₂O) or an organic salt, such as analkali metal salt of a C₁₋₄ alkanoic acid such as lithium acetate(LiC₂H₃O₂), lithium acetate dihydrate (LiC₂H₃O₂x2H₂O), or sodium acetateand the like; alkali metal salts of arylcarboxylic acids such as lithiumbenzoate, sodium benzoate, and the like; alkali metal salts of alkyl andaryl sulfonates such as sodium methylsulfonate and sodiump-toluenesulfonate and the like. Other types of salts and theirrespective hydrates include, but are not limited to, magnesium acetate,magnesium nitrate, sodium-based salts (such as sodium chloride, sodiumbromide and the like), lithium-based salts (such as lithium bromide,lithium carbonate, lithium chloride, etc.) and potassium-based salts.Many of these salts are commercially available from Aldrich ChemicalCompany, Milwaukee, Wis. See the Aldrich Catalog Handbook of FineChemicals 1996-1997. It is not intended that this list of salts is anexclusive or comprehensive list. These salts are disclosed as typicalexamples; The present invention is not restricted to the listed salts,as would be apparent to those of skill in the art.

The susceptor can also be an ionomer. Preferably, the ionomer alsofunctions as an adhesive and/or coating. Examples of such ionomersinclude without limitation styrenated ethylene-acrylic acid copolymer orits salts, sulfonated polyesters and their salts, sulfonated polystyreneand its salts and copolymers, polyacrylic acid and its salts andcopolymers, hydroxy/carboxylated vinylacetate-ethylene terpolymers,functionalized acrylics, polyesters, urethanes, epoxies, alkyds, latex,gelatin, soy protein, casein and other proteins, alginate, carrageenan,starch derivatives, ionic polysacharides, and the like. An example of anionomer that does not function as an adhesive is sodiumpolystyrenesulfonate.

Examples of ionomer adhesives are described in more detail below.

A. Sulfonated Polymers

Sulfonated polyesters and copolymers thereof are described in U.S. Pat.Nos. 5,750,605, 5,552,495, 5,543,488, 5,527,655, 5,523,344, 5,281,630,4,598,142, 4,037,777, 3,033,827, 3,033,826, 3,033,822, 3,075,952,2,901,466, 2,465,319, 5,098,962, 4,990,593, 4,973,656, 4,910,292,4,525,524, 4,408,532, 4,304,901, 4,257,928, 4,233,196, 4,110,284,4,052,368, 3,879,450, and 3,018,272. The invention relates tocompositions comprising sulfonated polyesters and copolymers thereof,e.g. as described in these patents, together with a polar carrier asdescribed herein as well as the adhesive compositions described in thesepatents (comprising the sulfonated polyesters and copolymers thereof)together with the polar carrier. Such sulfonated polyesters andcopolymers thereof are one preferred embodiment of the presentinvention, as such materials function both as an ionomeric susceptor andas an adhesive.

In a preferred embodiment, the sulfonated polyester is a higher Tg(about 48° C. to about 55° C. or higher) linear polyester which showsimproved heat resistance compared to lower Tg (about 35° C.) linear orbranched sulfonated polyesters. Once blended with the polar carrier, theTg of the resulting composition should be higher than the temperature atthe intended use, e.g. higher than body temperature for diaperadhesives. For example, a linear sulfonated polyester with a Tg of 55°C. (e.g. AQ55S) blended with a sufficient amount (greater than 10%) ofpolar carrier (e.g. glycerin) to achieve RF activity will result in a Tghigher than body temperature if the polar carrier is no more than about35% of the composition.

In another embodiment, a salt comprising a sulfonated polyester and acationic dye as described in U.S. Pat. No. 5,240,780, are employed. Suchsalts provide a colored susceptor composition that may be used, e.g. inprinting.

Sulfonated polyesters may be prepared by the polycondensation of thefollowing reactants:

(a) at least one dicarboxylic acid;

(b) at least one glycol;

(c) at least one difunctional sulfomonomer containing at least one metalsulfonate group attached to an aromatic nucleus wherein the functionalgroups may be hydroxy, carboxyl, or amino groups.

The dicarboxylic acid component of the sulfonated polyesters comprisesaliphatic dicarboxylic acids, alicyclic dicarboxylic acids, aromaticdicarboxylic acids, or mixtures of two or more of these acids. Examplesof such dicarboxylic acids include oxalic; malonic; dimethylmalonic;succinic; glutaric; adipic; trimethyladipic; pimelic;2,2-dimethylglutaric; azelaic; sebacic; fumaric; maleic; itaconic;1,3-cyclopentanedicarboxlyic; 1,2-cyclohexanedicarboxylic;1,3-cyclohexanedicarboxylic; 1,4-cyclohexanedicarboxylic; phthalic;terephthalic; isophthalic; 2,5-norbornanedicarboxylic; 1,4-naphthalic;diphenic; 4,4′-oxydibenzoic; diglycolic; thiodpropionic;4,4′-sulfonyldibenzoic; and 2,5-naphthalenedicarboxylic acids. Ifterephthalic acid is used as the dicarboxylic acid component of thepolyester, at least 5 mole percent of one of the other acids listedabove may also be used.

It should be understood that use of the corresponding acid anhydrides,esters, and acid chlorides of these acids is included in the term“dicarboxylic acid.” Examples of these esters include dimethyl1,4-cyclohexanedicarboxylate; dimethyl 2,5-naphthalenedicarboxylate;dibutyl, 4,4′-sulfonyldibenzoate; dimethyl isophthalate; dimethylterephathalate; and diphenyl terephthalate. Copolyesters may be preparedfrom two or more of the above dicarboxylic acids or derivatives thereof.

Examples of suitable glycols include poly(ethylene glycols) such asdiethylene glycol, triethylene glycol, tetraethylene glycol, andpentaethylene, hexaethylene, heptaethylene, octaethylene, nonaethylene,and decaethylene glycols, and mixtures thereof. Preferably thepoly(ethylene glycol) employed in the present invention is diethyleneglycol or triethylene glycol or mixtures thereof. The remaining portionof the glycol component may consist of aliphatic, alicyclic, and aralkylglycols. Examples of these glycols include ethylene glycol; propyleneglycol; 1,3-propanediol; 2,4-dimethyl-2-ethylhexane-1,3,diol;2,2-dimethyl-1,3-propanediol; 2-ethyl-2-butyl-1,3-propanediol;2-ethyl-2-isobutyl-1,3-propanediol; 1,3-butanediol; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; 2,2-4-trimethyl-1,6-hexanediol;thiodiethanol; 1,2-cyclohexanedimethanol; 1,3-cyclohexanedimethanol;1,4-cyclohexanedimethanol; 2,2,4,4-tetramethyl-1,3-cyclobutanediol;p-xylylenediol. Copolymers may be prepared from two or more of the aboveglycols.

The difunctional sulfo-monomer component of the sulfonated polyester mayadvantageously be a dicarboxylic acid or an ester thereof containing ametal sulfonate group or a glycol containing a metal sulfonate group ora hydroxy acid containing metal sulfonate group.

Advantageous difunctional sulfo-monomer components are those wherein thesulfonate salt group is attached to an aromatic acid nucleus such asbenzene, naphthalene, diphenyl, oxydiphenyl, sulfonyldiphenyl, ormethylenediphenyl nucleus. Particular examples include sulfophthalicacid, sulfoterephthalic acid, sulfoisophthalic acid,4-sulfonaphthalene-2,7-dicarboxylic acid, and their esters;metalosulfoaryl sulfonate having the general formula.

wherein X is a trivalent aromatic radical derived from a substituted orunsubstituted aromatic hydrocarbon, Y is a divalent aromatic radicalderived from a substituted or unsubstituted aromatic hydrocarbon, A andB are carboalkoxy groups containing 1 to 4 carbon atoms in the alkylportion or a carboxy group, the metal ion M is Li⁺, Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺,Ba⁺⁺, Cu⁺⁺, Fe⁺⁺, Fe⁺⁺⁻, and n is 1 for monovalent M or 2 for divalent Mor 3 for trivalent M. When a monovalent alkali metal ion is used, theresulting sulfonated polyesters are less readily dissipated by coldwater and more rapidly dissipated by hot water. When a divalent or atrivalent metal ion is used, the resulting sulfonated polyesters are notordinarily easily dissipated by cold water, but are more readilydissipated in hot water. Depending on the end use of the polymer, eitherof the different sets of properties may be desirable. It is possible toprepare the sulfonated polyester using, for example, a sodium sulfonatesalt and later by ion-exchange replace this ion with a different ion,for example, calcium, and thus alter the characteristics of the polymer.In general, this procedure is superior to preparing the polymer withdivalent metal salt inasmuch as the sodium salts may be more soluble inthe polymer manufacturing components than are the divalent metal salts.Polymers containing divalent or trivalent metal ions are less elasticand rubber-like than polymers containing monovalent ions. One suchmetallosulfoaryl sulfonate component may be prepared as shown by thefollowing general reactions:

and other chlorinating agents (e.g., thionyl chloride, phosphorustrichloride, phosphorous oxychloride) may be used. In addition, thereaction between the sulfonyl chloride and the sulfophenol may becarried out in water or an inert organic solvent, and the base used maybe an alkali metal hydroxide or a tertiary amine. Such suitablecompounds are disclosed in U.S. Pat. No. 3,734,874.

Optionally, the polycondensation reaction may be carried out in thepresence of one or more of the following:

(d) an unsaturated mono- or dicarboxylic acid; and,

(e) a difunctional hydroxycarboxylic acid having one —CH₂—OH group, anaminocarboxylic acid having one —NRH group, an amino alcohol having one—CR₂—CH and one —NRH group, a diamine having two —NRH groups, or amixture thereof, wherein each R is hydrogen or a C₁₋₄ alkyl group.

The α,β-unsaturated acids (d) are described by the following structure:

R—CH═CH—R¹

wherein R is H, alkylcarboxy, or arylcarboxy and R¹ is carboxy orarylcarboxy. Polymers derived from the above components can be used incombination with polymers derived from other components and/or incombination with other ethylenically unsaturated comonomers (e.g.,acrylic acid, acrylamide, butyl acrylate, diacetone acrylamide). Thecomonomers can be from 1-75 parts by weight, preferably 5-25 parts byweight αβ-unsaturated acids.

Advantageous difunctional components which are aminoalchohols includearomatic, aliphatic, heterocyclic and other types as in regard tocomponent (e). Specific examples include 5-aminopentanol-1,4-aminomethylcyclo-hexanemethanol, 5-amino-2-ethyl-pentanol-1,2-(4-β-hydroxyethoxyphenyl)-1-aminoethane, 3-amino-2, 2dimethylpropanol,hydroxyethylamine, etc. Generally these aminoalcohols contain from 2 to20 carbon atoms, one —NRH group and one —CR₂—OH group.

Such difunctional monomer components which are aminocarboxylic acidsinclude aromatic, aliphatic, heterocylic, and other types as in regardto component (c) and include lactams. Specific examples include6-aminocaproic acid, its lactam known as caprolactam,omegaaminoundecanoic acid, 3-amino-2-dimethylpropionic acid,4-(β-aminoethyl)benzoic acid, 2-(β-aminopropoxy)benzoic acid,4-aminomethylcyclohexanecarboxylic acid,2-(β-aminopropoxy)cyclohexanecarboxylic acid, etc. Generally thesecompounds contain from 2 to 20 carbon atoms.

Examples of such difunctional monomer component (e) which are diaminesinclude ethylenediamine; hexamethylenediamine;2,2,4-trimethylhexamethylenediamine; 4-oxaheptane-1,7-diamine;4,7-dioxadecane-1,10-diamine; 1,4-cyclohexanebismethylamine;1,3-cycloheptamethylene-diamine; dodecamethylenediamine, etc.

Greater dissipatability is achieved when the difunctional sulfo-monomerconstitutes from about 6 mole percent to about 25 mole percent out of atotal of 200 mole percent of (a), (b), (c), (d), and any (e) componentsof the polyester or polyesteramide. The total of 200 mole percent canalso be referred to as 200 mole parts.

Any of the above-identified difunctional monomers generally containhydrocarbon moieties having from 1 to about 40 carbon atoms in additionto their two functional groups, but they may in general also contain upto six non-functional groups such as —O—, —S—, —SO₂—, —SO₂—O—, etc. Forexample, the poly(ethylene glycol) monomer used may contain from 1 toabout 19 oxy groups, such as —O— groups.

In a preferred embodiment, the ionomer is one of the sulfonatedpolyesters sold by Eastman Chemical Company, Kingsport, Tenn. (hereafter“Eastman”) which are water dispersible, linear or branched polyestersformed by the polycondensation of glycols with dicarboxylic acids, someof which contain sodiosulfo groups. Sulfopolyester hybrids may also beemployed which are formed by the in situ polymerization of vinyl and/oracrylic monomers in water dispersions of SULFOPOLYESTER. Such Eastmansulfonated polyesters may be purchased from Eastman under nos. AQ1045,AQ1350, AQ1950, AQ14000, AQ35S; AQ38S, AQ55S and EASTEK 1300.

The sulfonated polyesters and copolymers thereof may range from about 10to about 90 weight percent, more preferably, about 60 to 80 weightpercent, most preferably about 70 weight percent of the totalcomposition. The polar carrier may range from about 10 to about 90weight percent, more preferably, about 20 to about 40 weight percent,most preferably, about 30 weight percent of the total composition. Theremainder of the composition may comprise one or more of the otheradditives described herein.

Compositions comprising branched sulfonated polyesters tend to giveclear, tacky and flexible films. Compositions comprising linearpolyesters tend to give clear or white, tack-free, flexible films.

Other sulfonated polymers that can be used in the practice of theinvention include polystyrene sulfonate, acrylaminopropane sulfonate(AMPS) based polymers (e.g. 2-acrylamido-2-methylpropanesulfonic acidand its sodium salt available from Lubrizol Process Chemicals). Inaddition, urethane ionomers can be prepared by reacting a diisocyanatewith a diol that has sulfonate functionality (e.g. butane diolsulfonate).

B. Acrylic Acid and Maleic Anhydride Polymers and Copolymers

Other ionomers include acrylic acid polymers and copolymers and saltsthereof. Such polymers and copolymers are described in U.S. Pat. Nos.5,821,294, 5,717,015, 5,719,244, 5,670,566, 5,618,876, 5,532,300,5,530,056, 5,519,072, 5,371,133, 5,319,020, 5,037,700, 4,713,263,4,696,951, 4,692,366, 4,617,343, 4,948,822, and 4,278,578.

The invention relates to compositions comprising the acrylic acidpolymers and copolymers thereof described in these patents together witha polar carrier as described herein as well as the adhesive compositionsdescribed in these patents (comprising the acrylic acid polymers andcopolymers thereof) together with the polar carrier.

Specific examples of such acrylic acid copolymers include ethyleneacrylic acid copolymer and the ammonium (MICHEM 4983P) and sodium(MICHEM 48525P) salts thereof available from Michelman Incorporated,Cincinnati, Ohio A further example is vinyl acetate acrylic copolymers(e.g. ROVACE HP3442) available from Rohm and Hass, Philadelphia, Pa.

The acrylic acid polymers and copolymers may range from about 10 toabout 90 weight percent, more preferably, about 40 to 80 weight percent,most preferably about 50-70 weight percent of the total composition. Thepolar carrier may range from about 10 to about 90 weight percent, morepreferably, about 10 to about 40 weight percent, most preferably, about30 weight percent of the total composition. The remainder of thecomposition may comprise one or more of the other additives describedherein.

Compositions comprising ethylene acrylic acid copolymers and a polarcarrier tend to give clear, colorless, tack-free films with very goodadhesion that heat in well under one second when exposed to RF. Vinylacetate acrylic copolymer compositions tend to give clear, colorless,flexible but very tacky films with very good adhesion that heat in wellunder one second when exposed to RF.

In a preferred embodiment, compositions comprising acrylic acid polymersor coplymers are applied as liquid dispersions and dried into an RFsusceptive coating.

Alternatively, maleic anhydride based copolymers such styrene maleicanhydride, ethylene maleic anhydride, and popylene maleic anhydride(available from Eastman Chemicals) may be employed as an ionomer. Suchcompositions are preferably applied as an aqueous dispersion at roomtemperature and dried into an RF susceptive coating.

C. Starch/Polysaccharide Derivatives

Other ionomers include starch and polysaccharide derivatives such aspolysulfonated or polysulfated derivatives, including dextran sulfate,pentosan polysulfate, heparin, heparan sulfate, dermatan sulfate,chondroitin sulfate, a proteoglycan and the like. Dextran sulfate isavailable from Sigma Chemical Corporation,. St. Louis, Mo., withmolecular weights of 10,000, 8,000 and 5,000. Examples of other ionicpolysaccharides include carrageenan, chitosan, xanthan gum, etc.

Phosphorylated starch as disclosed in U.S. Pat. No. 5,329,004 may beemployed as a susceptor.

The starch/polysaccharide derivatives may range from about 10 to about90 weight percent, more preferably, about 60 to 80 weight percent, mostpreferably about 70 weight percent of the total composition. The polarcarrier may range from about 10 to about 90 weight percent, morepreferably, about 20 to about 40 weight percent, most preferably, about30 weight percent of the total composition. The remainder of thecomposition may comprise one or more of the other additives describedherein.

D. Proteins

Other ionomers include proteins such as gelatin, soy protein, casein,etc. Gelatin is the purified protein derived from the selectivehydrolysis if collagen. Collagen is the principal organic component ofthe bones and skin of mammals. Common raw materials include bones,cattle hides and pigskins. Gelatins are classified as either acid type(A type) or limed (B type) according to the process by which they aremade. Particular examples of gelatins include KNOX gelatin as well astypes P, D, D-I, LB, LM and K, available from PB Gelatins. See also thegelatin described in U.S. Pat. No. 5,877,287. In a preferred embodiment,the gelatin is 45Y56-853-3V0-6CS, available from Eastman Gelatin,Peabody, Mass. Alternatively, a gelatin-modified polyurethane asdisclosed in U.S. Pat. No. 5,948,857 may be used.

In a preferred embodiment, the pH of the gelatin is raised or lowered inorder to enhance the ionomeric character of the gelatin. The pH may beraised by the addition of aqueous base to an aqueous solution orsuspension of the gelatin. Examples of suitable bases include alkalimetal hydroxides, alkali metal carbonates and bicarbonates, alkali metalacetates, ammonia, amino compounds such as methylamine, dimethylamine,trimethylamine, triethylamine, and the like. Alternatively, a basicbuffer solution may be added, e.g. a solution comprising2-amino-2-methyl-1-propanol; or a glycine buffer at pH 9.4 and 10.4;each of which is available from Sigma Chemical Corporation, St. Louis,Mo. Other buffers include 0.01 borax (pH 9.2), TRIS (pH 7-9.1 dependingon concentration), 0.05 M carbonate (pH 9.93), and 0.05 M trisodiumphosphate (pH 12). See “The Chemist's Companion,” A. J. Gordon and R. A.Ford, John Wiley & Sons, New York, N.Y., 1972. The pH may be lowered bythe addition of an acid such as HCl, HBr, H₂SO₄, H₃PO₄, or an organicacid such as C₁₋₄ alkanoic acid (e.g. acetic acid, propionic acid orbutyric acid), an arylcarboxylic acid (e.g. benzoic acid), orarylsulfonic acid (e.g. p-toluenesulfonic acid). Alternatively, anacidic buffer may be added, e.g. acetate buffer at pH 4.5, 4.9 and 5.0;citrate buffer at pH 4.8; or a phosphate-citrate buffer at pH 5.0; eachof which is available from Sigma Chemical Corporation. Other buffersinclude 0.005 M potassium tetraoxalate (pH 1.7), saturated potassiumtartrate (pH 3.6), 0.05 M potassium phthalate (pH 4.0), and 0.05 Msodium succinate (pH 5.3). See “The Chemist's Companion,” A. J. Gordonand R. A. Ford, John Wiley & Sons, New York, N.Y., 1972. As discussed inthe Examples, it has been discovered unexpectedly that when the pH ofthe gelatin composition is shifted into the acidic or basic range, thecomposition exhibits enhanced heating in an RF field compared to theuntreated gelatin. The best heating occurs when the pH is low. Suchgelatin compositions give flexible films that attach well to substratesand heat in under one second.

In a preferred embodiment, the pH of the gelatin may range from about 8to about 12. In a most preferred embodiment, the pH of the gelatin isabout 10. In another preferred embodiment, the pH of the gelatin mayrange from about 1 to about 6. In a most preferred embodiment, the pH ofthe gelatin is about 2.

The gelatin may range from about 10 to about 90 weight percent, morepreferably, about 60 to 80 weight percent, most preferably about 70weight percent of the total composition. The polar carrier may rangefrom about 10 to about 90 weight percent, more preferably, about 20 toabout 40 weight percent, most preferably, about 30 weight percent of thetotal composition. The remainder of the composition may comprise one ormore of the other additives described herein.

E. Others

Other ionomers that may be used in the practice of the invention includesulfonated novolak resins obtained by a process comprising reacting anaromatic compound with a sulfonated agent to form a sulfonated aromaticcompound, condensing the sulfonated aromatic compound with anon-sulfonated phenolic compound and an aldehyde or aldehyde precursorto form a sulfonated condensate, and reacting the condensate with amonovalent or divalent metal oxide, hydroxide, carbonic acid, boronicacid or carboxylic acid. See U.S. Pat. No. 5,098,774. Other ionomersthat can be used are lignosulfonates and their sodium salts which areavailable with different molecular weights and levels of sulfonationfrom Westvaco, North Charleson, S.C.

In addition, urethane ionomers can be prepared by reacting adiisocyanate with a diol that has carboxy functionality (e.g.dimethylol).

III. The Polar Carrier

In a preferred embodiment, the ionomer is combined with a carrier thatis a flowable polar compound, such as a polar solvent, having a highdielectric constant, e.g. ∈ (20° C.) ≧about 10, more preferably, ≧about20. A preferred dielectric constant range is about 13-63 (25° C.), morepreferably, about 17-43 (25° C.). It has been unexpectedly discoveredthat compositions comprising an ionomer and such a carrier heat muchmore rapidly when exposed to RF energy, even at low levels, compared towhen the ionomer or carrier are exposed separately. Without being boundby any particular theory, it is believed that upon exposure to RFenergy, the polar carrier allows for the migration and/or vibration ofprotons or metal ions from the ionomer, resulting in the generation ofheat.

Such polar carriers include, but are not limited to, water,dimethylformamide (DMF), dimethylacetamide (DMAC), dimethylsulfoxide(DMSO), tetrahydrofuran (THF), polypropylene carbonates, ketones (suchas acetone, acetyl acetone, cyclohexanone, diacetone alcohol, andisophorone), alcohols (such as ethanol, propanol, 2-methyl-1-propanol,and the like) amino alcohols (such as ethanolamine), oxazolidines,polyols, organic acids (such as formic, acetic, propionic, butyric anddimethylol butyric acid and the like), anhydrides (such as aceticanhydride and maleic anhydride), amides (such as formamide, acetamideand propionamide), nitriles (such as acetonitrile and propionitrile),and nitro compounds (such as nitrobenzene, nitroaniline, nitrotoluene,nitroglycerine and any of the nitroparaffins). Any polar carrier thatcan weaken, to some degree, the ionic interaction between the anion andcation of the ionic susceptor, even if the susceptor component is anon-ionic compound, may be utilized in the present invention. Preferredpolar carriers are humectants (e.g., glycerin, 1,2-propanediol andpolyethyleneglycol), i.e., they retain at least a low level of moistureafter application. It is believed that the low level of residualmoisture enhances the RF activation of the compositions.

Examples of polyols that may be used as a polar carrier include glycolssuch as diethylene glycol, triethylene glycol, tetraethylene glycol,dipropylene glycol, thioethylene glycol, and pentaethylene,hexaethylene, heptaethylene. octaethylene, nonaethylene, anddecaethylene glycols, and mixtures thereof, as well as aliphatic,alicyclic, and aralkyl glycols. Particular examples of these glycolsinclude ethylene glycol; 1,2-propylene glycol; 1,3-propanediol;2,4-dimethyl-2-ethylhexane-1,3,diol; 2,2-dimethyl-1,3-propanediol;2-ethyl-2-butyl-1,3-propanediol; 2-ethyl-2-isobutyl-1,3-propanediol;1,3-butanediol; 1,4-butanediol: 1,5-pentanediol; 1,6-hexanediol;2,2-4-trimethyl-1,6-hexanediol; thiodiethanol.1,2-cyclohexanedimethanol; 1,3-cyclohexanedimethanol;1,4-cyclohexanedimethanol; 2,2,4,4-tetramethyl-1,3-cyclobutanediol;p-xylylenediol.

Also included are polyethylene glycols, e.g. having weight averagemolecular weights ranging from about 400 to about 2,000; mixedpoly(ethylene)-poly(propylene) glycols having weight average molecularweights ranging up to about 6,000 and containing from about 30 to about90 weight percent ethylene oxide; the monomethyl, monoethyl andmonobutyl ethers of ethylene glycol, propylene glycol and diethyleneglycol, the monomethyl and monoethyl ethers of triethylene glycol; thedimethyl and diethyl ethers of diethylene glycol, dipropylene glycol andtrimethylene glycol. Examples of polyols containing three or morehydroxy groups include glycerin and derivatives of glycerin such asglycerol mono-, di-, and triacetate, or monomethacrylate. Also includedis polyvinylalcohol, which also functions as an adhesive compound.Polyvinylalcohols of molecular weights 89,000-98,000, 85,000-146,000,124,000-186,000, 31,000-50,000, 85,000-146,000, 124,000-186,000,13,000-23,000, 50,000-85,000, with various levels of hydrolysis, areavailable from Aldrich Chemical Company.

The polar carrier may also be an alkanolamine and substitutedalkanolamine based on ethanol and isopropanol such as mono-, di- andtriethanolamine; mono-, di- and triisopropanolamine, methylethanolamine,dibutylethanolamine, phenyldiethanolamine,di-(2-ethylhexyl)ethanolamine, dimethylisopropanolamine,dibutylisopropanolamine, and the like as well as mixtures thereof.

N-Alkyl sulfonamides are also useful carriers.

The present invention is not restricted to the listed carriers, andmixtures of carriers may be utilized, as would be apparent to those ofskill in the art. Such polar carriers may comprise about 10 to 90 weightpercent of the composition. In a preferred embodiment, the polar carriercomprises about 30 weight percent of the total composition. In a morepreferred embodiment, the polar carrier comprises about 13-30% weightpercent, more preferably, about 15-25 weight percent, most preferably,about 20-23 weight percent. At these percentages, very short heatingtimes are possible while retaining acceptable shear strength of thebond.

Preferable high dielectric constant carriers are those that can generateheat without being highly volatile, in order to preserve RF susceptormobility in the composition. Preferred carriers are glycols such asglycerine and N-methyl pyrrolidone (NMP). NMP has a high dipole momentof 4.09 Debye, which produces a dielectric constant, K, of 32.2 at 25°C. NMP is noncorrosive, biodegradable, and almost odorless. NMP has alow order of oral toxicity and is neither a skin irritant nor asensitizer. NMP is also an excellent solvent both for a wide range oforganic compounds and polymers, as well as for some inorganic salts. Inshort, it is a very useful medium for dissolving or dispersingsusceptors and film formers that are employed in the bonding or adheringof substrates or layers according to the present invention.

A further preferred high dielectric constant carrier is glycerine.Glycerine has a dielectric constant of 42.5 at 25° C., is noncorrosive,biodegradable, and odorless. Glycerine is nontoxic and is neither a skinirritant nor a sensitizer. Thus, glycerine is a preferred carrier forconsumer products containing adhesives and coatings. Glycerine is alsoan excellent solvent both for a wide range of organic compounds andpolymers, as well as for some inorganic salts.

A suitable susceptor composition according to the present inventioncomprises a susceptor present in a concentration of from about 10% toabout 50) % and a carrier present in a concentration of from about 1% toabout 75%. Additionally, another suitable susceptor composition furthercomprises an adhesive compound or other additive as described hereinpresent in a concentration of from about 10% to about 35%. The susceptorcomposition can be used to bond or adhere substrates or layers to oneanother. The substrates can include single layers of polyolefins andnon-polyolefins, as well as multilayer stacks. Such stacks may comprise2, 3, 4, 5 or more layers. One or more susceptor compositions, which maybe the same or different, may be between 2 or more layers of themultilayer stacks. All composition concentrations described hereincorrespond to weight-weight percentages, unless indicated otherwise.

IV. Further Additives to the Susceptor Compositions

A number of different additives may be added to the susceptorcompositions of the present invention including the carrier or mobilemedium. In order to provide uniform heating of a susceptor composition,the susceptors are dissolved, distributed, or dispersed, preferablysubstantially uniformly, in a carrier containing either various polymersand/or solvents or plastisizers. Some carriers, such as solvents,plastisizers, or polymers, are utilized for their polar functionalityand for their ability to enhance the heating process.

A. Adhesive/Thermoplastic Additives

The adhesive properties of the susceptor composition of the presentinvention are enhanced by the presence of one or more thermoplastic oradhesive compounds, such as polymers or copolymers, that are blended inthe susceptor composition. Some of the thermoplastic or adhesivecompounds utilized in the present invention include, but are not limitedto, polyesters such as a thermoplastic methylol polyester prepared fromthe reaction of at least one dicarboxylic acid with a diglycidyl ether,a diglycidyl ester or combination thereof (see U.S. Pat. No. 5,583,187)or a cyanoacrylate/polyester adhesive composition (see U.S. Pat. No.5,340,873); polyamides; polyurethanes (see U.S. Pat. No. 5,391,602);polysiloxanes; elastomers; polyvinylpyrrolidone; ethylene vinyl acetatecopolymers (see U.S. Pat. No. 4,460,728), vinylpyrrolidone vinyl acetatecopolymers; vinyl ether copolymers (e.g. polyvinyl methyl ether);polyvinyl alcohol; partially hydrolyzed polyvinyl acetate; copolymerscomprising a starch ester (see U.S. Pat. No. 5,498,224) and starchhydrolysates (see U.S. Pat. No. 5,827,553); graft copolymer preparedfrom a vinyl monomer and a polyalkylene oxide polymer, and ahydroxy-containing ester or acid wax (see U.S. Pat. No. 5,852,080);copolymers comprising a graft copolymer prepared from a vinyl monomer,at least one polyalkylene oxide polymer, a polar wax and other optionalingredients (see U.S. Pat. No. 5,453,144); thermoplastic blockcopolymers comprising an aromatic vinyl copolymer block, a diene polymeror hydrogenated derivative thereof and other additives (see U.S. Pat.No. 5,723,222); vinyl chloride copolymers; vinylidene chloridecopolymers; vinylidene fluoride copolymers; vinyl pyrrolidone homo- andcopolymers; vinyl pyridine homo- and copolymers; hydrolyzed- polyvinylalcohol and compositions thereof (see U.S. Pat. No. 5,434,216);cellulose esters (e.g. cellulose acetate and starch acetate, see U.S.Pat. No. 5,360,845) and ethers (e.g. hydroxypropyl cellulose, methylcellulose, ethyl cellulose, propyl cellulose and the like; see U.S. Pat.No. 5,575,840, 5,456,936 and 5,356,963); modified starch estercontaining adhesives (see U.S. Pat. No. 5,360,845); high amylase starchcontaining adhesive (see U.S. Pat. No. 5,405,437); poly-alphaolefins;propylene homo- and copolymers; ethylene homo- and copolymers(especially those of vinyl acetate, vinyl alcohol, ethyl- andbutyl-acrylate, carbon monoxide, acrylic and methacrylic acid, crotonicacid, and maleic anhydride), an alkyl acrylate hot melt adhesive (seeU.S. Pat. No. 4,588,767), a hot melt adhesive comprising an alkylacrylate and an alpha-olefin (see U.S. Pat. No. 4,535,140), a hot meltadhesive comprising an ethylene n-butyl acrylate copolymer (see U.S.Pat. No. 5,331,033), a hot melt adhesive comprising a graft copolymercomprising at least one vinyl monomer and at least one polyalkyleneoxide polymer (see U.S. Pat. No. 5,217,798), a vinyl acetate copolymercopolymerized with a cyclic ureido compound (see U.S. Pat. No.5,208,285), a hydrophilic polycarbodiimide (see U.S. Pat. No.5,100,994), a photopolymerized, pressure sensitive adhesive comprisingan alkyl acrylate, a monethylenically unsaturated polar copolymerizablemonomer, ethylene vinylacetate copolymer and a photo initiator (see U.S.Pat. No. 5,079,047), a hot melt adhesive comprising tackifying resins,oil diluent, and a substantially radial styrene-butadiene blockcopolymer (U.S. Pat. No. 4,944,993), an adhesive prepared from the vinylester of an alkanoic acid, ethylene, a dialkyl maleate, an N-methylolcomonomer, and an ethylenically unsaturated mono- or dicarboxylic acid(see U.S. Pat. No. 4,911,960), an adhesive prepared from the vinyl esterof an alkenoic acid, ethylene, a dialkyl maleate, and a monocarboxylicacid (see U.S. Pat. No. 4,892,917), a hot melt adhesive consistingessentially of an ethylene n-butyl acrylate copolymer (U.S. Pat. No.4,874,804), hot melt adhesive compositions prepared fromstyrene-ethylene-butylene-styrene tri-block and/orstyrene-ethylene-butylene di-block copolymers that are tackified (U.S.Pat. No. 4,822,653), a hot melt packaging adhesive comprising a ethylenen-butyl acrylate copolymer with n-butyl acrylate (U.S. Pat. No.4,816,306), polysaccharide esters containing acetal and aldehyde groups(U.S. Pat. No. 4,801,699), polysaccharide aldehyde derivatives (U.S.Pat. No. 4,788,280), an alkaline adhesive comprising a latex polymer ora halohydrin quaternary ammonium monomer and starch (U.S. Pat. No.4,775,706), polymeric fatty acid polyamides (U.S. Pat. No. 4,419,494),hot melt adhesives comprising resins containing 2-methylstyrene, styreneand a phenol (U.S. Pat. No. 4,412,030). The present invention is notrestricted to the listed adhesive compounds and compositions, as wouldbe apparent to those of skill in the art.

Such adhesive additives may comprise about 1 to 50 weight percent of thecomposition, more preferably, about 25 weight percent.

B. Adhesive/Coating Thermoset Additives

It is also possible to add a thermoset resin to the susceptorcompositions of the present invention. Such thermosets are capable ofbeing cross-linked or cured through heat and/or catalysts and includethose described in U.S. Pat. No. 5,182,134, e.g. epoxies, polyurethanes,curable polyesters, hybrid thermosets, and curable acrylics. Othersinclude bismaleimides, silicons, phenolics, polyamids and polysulfidesamong others. Further examples include maleate resins formed by thereaction of various polyols with maleic anhydride. Orthophthalic resinsmay be used which are formed by the reaction of phthalic anhydride andmaleic anhydride or fumaric anhydride as the dibasic acid.. Isophthalicresins may also be used which may be formed by reacting isophthalic acidand maleic anhydride. Others include the bis-phenol fumarides,chlorendic polyester resins, vinyl esters, dicyclopentadiene resins,orthotolyl biguanine, the diglycidyl ether formed from bis-phenol A andepichlorohydrin, triglycidyl isocyanurate thermosetting compositions,bis-phenol A-epichlorohydrin diglycidyl ether cured with phenoliccross-linking agents, aliphatic urethane thermosetting compositions suchas an unblocked isofuron diisocyanate-E-caprolactam, BTDA thermosettingcompositions which are generally the reaction product of3,3,4,4-benzophenone tetracarboxylic dianhydride and a bis-phenolA-epichlorohydrin diglycidyl ether, hybrid thermosetting compositionswhich are the reaction product of a carboxylated saturated polyestercuring agents and bis-phenol A-epichlorohydrin diglycidyl ether,standard bis-phenol A-epichlorohydrin diglycidyl thermosets such asthose which are cured from 2-methylimidazole, and standard bis-phenolA-epichlorohydrin diglycidyl ether thermosets which are cured with2-methylimidazole and dicyandiamide thermosetting compositions. See U.S.Pat. Nos. 5,182,134, 5,387,623

Other thermosets and adhesives/coatings that may be added to thesusceptor compositions of the invention include a reactive polyurethaneprepolymer and 2,2′-dimorpholinoethylether ordi(2,6-dimethylmorpholinylethyl) ether catalyst (see U.S. Pat. No.5,550,191), a free radical polymerizable acrylic monomer, diazoniumsalt/activator composition (see U.S. Pat. No. 4,602,073), adiphenylmethane diisocyanate, a caprolactone triol, a neopentyl adipateester diol, and, optionally, at least one polypropylene diol togetherwith a catalyst (U.S. Pat. No. 5,057,568), an aqueous polyurethanedispersion comprising an isocyanate-terminated polyurethane prepolymercontaining carboxylic acid salt groups, and an active hydrogencontaining chain extender (U.S. Pat. No. 4,801,644).

The susceptor compositions of the present invention may also be combinedwith a shelf stable thermosetting resin as described in U.S. Pat. No.5,739,184, which is then activated by RF energy to give coatings, e.g.for wood or paper products. This thermosetting resin comprises an epoxyresin, a rosin and an organometallic compound in an amount effective toprovide improved adhesion to wood or paper substrates.

Curing agents may also be combined together with the susceptor/thermosetcompositions of the invention, including melamines such as dialkylmelamines, amides such as dicyandiamide, adipamide, isophthalyl diamide,ureas such as ethylene thiourea or guanylurea, azides such asthiosemicarbazide, azoles such as guanazole or 3-amino-1,2,4-triazole,and anilines such as dialkylanilines such as dimethyl aniline anddiethyl aniline.

Such thermoset additives may comprise about 1 to 50 weight percent ofthe composition, more preferably, about 25 weight percent.

It has also been discovered that thermoset compositions may be activatedwith only the polar carrier and without a susceptor. Thus, the inventionalso relates to compositions comprising a thermoset and a polar carrier.The thermoset may comprise about 60 to 95 weight percent of such acomposition. The polar carrier may comprise about 5 to 40 weightpercent. The invention relates as well to methods of bonding, adheringor coating substrates with such thermoset/polar carrier compositions.

C. Surfactant Additives

According to another embodiment of the present invention, surfactantadditives can be added to the susceptor composition to enhance theability to draw down the susceptor composition of the present inventiononto the layers or substrates to be bonded, adhered or coated. Dependingon the types of materials that are to be joined or coated, surfactantadditives, such as SURFYNOL 104PA (available from Air ProductsCorporation) and SURFADONE LP 300 (N-dodecyl-2-pyrrolidone, availablefrom International Specialty Products), can be used to wet a variety ofsubstrates such as Mylar and polyethylene (PE). A further plasticizer isp-toluenesulfonamide, a good plasticizer that also dissolves stannouschloride. The present invention is not restricted to the listedsurfactant additives, as would be apparent to those of skill in the art.Such surfactants may comprise about 0.1 to 5 weight percent of thecomposition.

D. Plasticizer Additives

The susceptor compositions of the present invention may further comprisea plasticizer to modify the flexibility of the adhesive or coating.Examples of such plasticizers include, but are not limited to acetyltributyl citrate, butyl benzyl phthalate, butyl phthalyl butylglycolate, dibutyl phthalate, dibutyl sebacate, diethyl phthalate,diethylene glycol dibenzoate, dipropylene glycol, dipropylene glycoldibenzoate, ethyl phthalyl ethyl glycolate, ethyl-p-toluene sulfonamide,hexylene glycol, methyl phthalyl ethyl glycolate, polyoxyethylene arylester, tributoxyethyl phthalate, triethylene glycol polyester of benzoicacid and phthalic acid, glycerin, or mixtures thereof. Otherplasticizers that may be used include N-methyl-2-pyrrolidone (NMP), andsubstituted toluene sulfonamides (e.g. p-toluenesulfonamide, RIT-CIZER#8™ and RIT-O-LITE MHP™ from Rit-Chem Co., Inc., Pleasantville, N.Y.).Such plasticizers may comprise about 1 to 40 weight percent of thecomposition.

E. Tackifiers

The tackiness of the compositions of the invention may be increased bythe addition of a suitable tackifier, e.g. one or more of hydrogenatedaromatic petroleum resins, hydrogenated aliphatic petroleum resins, andhydrogenated terpene resins (see U.S. Pat. No. 5,418,052),coumarone-indene, ester gum, gum rosin, hydrogenated rosin, phenolicmodified hydrocarbon resins, rosin esters, tall oil rosins, terpenephenolic, terpene resins, toluene sulfonamide-formaldehyde resin, woodrosin (see U.S. Pat. No. 5,442,001), distilled rosin, dimerized rosin,maleated rosin, polymerized rosin (see U.S. Pat. No. 5,532,306). Othertackifiers and modifiers, include (but are not limited to) styrene andalpha methyl styrene resins, glycerol and pentaerithritol esters, etc.Particular tackifiers include WINGTACK 95 from Goodyear, Herculin D andPICCOLYTE C from Hercules, EASTOTACK H100 from Eastman, and ECR 149B orECR 179A from Exxon Chemical (see U.S. Pat. No. 5,559,165). Othertackifiers include rosin and its derivatives available from ReicholdChemicals, Manila Copal (softening point 81-90° C. acid No. 110-141),Pontianac (softening point 99-135° C. acid No. 1120129) and Sanarec(softening point 100-130° C., acid no. 117-155). Such tackifiers maycomprise about 1 to 25 weight percent of the composition.

F. Fillers

A number of different fillers may be added to the susceptor compositionsof the invention, including, but not limited to cellulose, bentonite,calcium carbonate, calcium silicate, clay, mica silica, talc, alumina,glass beads, fibers and the like. Such fillers may comprise about 0 to40 weight percent of the composition.

G. Stabilizers and Antioxidants

Stabilizers and antioxidants may be added to the susceptor compositionsof the invention in amounts effective to achieve the intended result.Included among such stabilizers include high molecular weight hinderedphenols and multifunctional phenols such as sulfur andphosphorous-containing phenols. Representative hindered phenols include1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,pentaerythritol tetrakis-3-(3,5-di-tert-butyl-4-hydroxypropionate,n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenyl)propionate,4,4′-methylenebis(2,6-di-tert-butylphenol), 4,4′-thiobis(6-tert-butyl-o-cresol), 2,6-di-tert-butylphenol,6-(4-hydroxyphenoxy)-2,4-bis(n-octylthio)-1,3,5-triazine,di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate,2-(n-octylthio)ethyl-3,5di-tert-butyl-4-hydroxybenzoate, and sorbitolhexa[3-(3,5-di-tert-butyl 4-hydroxylphenyl)propionate (see U.S. Pat. No.5,574,076). Such stabilizers and antioxidants may comprise about 0.01 to5 weight percent of the composition.

H. Other additives

According to another embodiment of the present invention, other types ofadditives to the susceptor composition may include flow aids, heat andUV stabilizers, coupling agents, waxes, pigments and other organiccompounds. For example, in some instances, waxes can facilitate lowermelt temperatures. Waxes that can be utilized include, but are notlimited to, Bees wax (SYNCHROWAX BB4), Candelilla wax, CARBOWAX 3350(available from Union Carbide Corporation), Carnauba wax, and CASTORWAXNF. Other waxes include N-(2-hydroxyethyl)-2,2′-ethylene-bis-stearamide,stearamide, 12-hydroxystearamide wax, hydrogenated castor oil, oxidizedsynthetic waxes, poly(ethylene oxide) having a molar average molecularweight of above about 1000, and functionalized synthetic waxes such ascarbonyl containing ESCOMER H101 from Exxon (see U.S. Pat. No.5,532,306). Preferably, the wax polar as described in U.S. Pat. No.5,750,605. A preferred polar wax is Peracin 200. Also preferably, thepolar wax is present at no more than about 25%, more preferably, no morethan 17% of the composition, most preferably, no more than 10% of thecomposition.

Other additives include elastomers such as those described in U.S. Pat.No. 5,506,298, 5,739,184, 5,169,890, 5,039,744, 4,761,198 may be used,including styrene butadiene rubber, polybutadiene rubber, rubber,nitrile rubbers, butyl rubber and halogenated butyl rubber.

When the compositions are applied and activated as coatings, they mayfurther comprise one or more additives to impart color to thecomposition. Such additive include, without limitation, titaniumdioxide, iron oxide pigments, carbon black and organic pigments such asisoindoline yellow.

The present invention is not restricted to the listed additives, aswould be apparent to those of skill in the art. Such other additives maycomprise about 1 to 25 weight percent of the composition.

V. Applying the Susceptor Compositions to Substrates

The compositions of the invention may be formulated to be applied as aliquid at room temperature, hot melt, or powder. Liquid compositions maybe solvent borne or water-borne. The liquid applied compositions may beapplied as a liquid at room temperature and dried down to give thedesired coating. The liquid applied coating may be applied to asubstrate by any conventional method including spraying, ink-jet,brushing, rolling, gravure printing, dripping and the like. Methods ofactively drying down liquid compositions include but are not limited toconventional oven drying, forced air, heat lamps, microwave heating, RFheating or various combinations of these or other methods. When a liquidcomposition is dried down, it loses some or all of its volatiles. RFdrying of a liquid applied composition may be accomplished by applyingRF energy across the composition in order to generate sufficient heatwithin the liquid to facilitate or enhance the evaporative loss of wateror solvent(s). The RF energy can be applied across the liquid atconstant, intermittent, or gradient intensities to achieve the desiredrate and degree of drying. Similarly, other methods of drying may beapplied at constant, intermittent or gradient intensities to achieve thedesired drying result.

Hot melt applied systems are applied in their molten state at anelevated temperature and then cooled to yield the desired solid coating.The hot melt compositions can be heated to a molten state by variousmethods including but not limited to conventional melt tanks, microwaveheating and RF heating. Once the hot melt composition is melted, it maybe applied in a variety of different types of hot melt coatings,including but not limited to spirals and beads, hot blown, slot coat,and co-extrusion. After application, the molten hot melt composition canbe passively or actively cooled to return to its solid form. Activecooling may be accomplished by blowing cool air across the appliedmaterial, or by allowing the substrate to make contact with a heat-sinksurface.

Powdered applied systems are applied in their “fine” particle -state(1-20 μm) by electrostatic spray or gun. The applied layer is activatedby RF energy as in liquid or hot-melt systems.

Once dried and/or cooled, the substrate may be stored until activationof the composition is desired. Many of the applied compositions of theinvention are substantially non-tacky and may be applied to a substratewhich is then rolled up. Upon unrolling and activating, the substratemay be adhered to one or more other substrates. Those compositions thatare tacky may be activated immediately after being applied and dried ifnecessary. Alternatively, they may be covered with a removable strip ordusted with talc or similar material.

One aspect of the invention also relates to a method for applying asusceptor composition to a substrate, comprising:

(1) formulating the susceptor composition as a liquid dispersion;

(2) applying the liquid dispersion of the susceptor composition to thesubstrate;

(3) drying the susceptor composition, wherein the drying step includesthe step of applying RF energy across the composition, therebygenerating heat within the liquid dispersion. In a preferred embodiment,one may roll up the substrate after the susceptor composition has dried.

The susceptor compositions may be applied to any conventional substratesincluding, without limitation, woven and nonwoven substrates such aspolyolefins, such as PP and PE webs, non-wovens, films and the like,cellulose substrates prepared from, for example, wood pulp (such aspaper, cardboard and the like), cotton fibers (e.g. textiles such ascloth, sheeting and industrial fabrics), glass, ceramic surfaces, rubberand synthetic polymeric substrates such as polyester or polyolefinsubstrates prepared from, for example, polypropylene and polyethylene,polyvinyl alcohol, polyhydroxyvalerate butyrate, polylactides,cellulosics, polyamides, polyvinyl chloride, polystyrene, acrylics,synthetic textile products, etc. and any combination of theaforementioned. Other substrates include metal (e.g. aluminum foil andother metal foils), wood, composites, etc.

VI Apparatus For Activating the Various Compositions of the PresentInvention

Generally, the compositions of the present invention may be heated(i.e., activated) by any system capable of generating an electromagneticfield of sufficient strength and frequency.

FIG. 4 illustrates a high level block diagram of an RF heating system400 that is capable of generating an electromagnetic field foractivating the compositions of the present invention. Heating system 400includes an RF power supply 402 that provides about a 1 kW, 1 to 15 MHz,RF signal 404 to a heat station 406. Heating system 400 also includes aninductor 408 that is coupled to RF power supply 402 through heat station406. Generally, heat station 406 includes a capacitor connected eitherin series with or parallel to inductor 408.

RF signal 404 provided to heat station 406 by RF power supply 402creates an alternating current flowing through inductor 408, whichcreates an electromagnetic field. Heating of a sample 410, which is orincludes a composition of the present invention, occurs when sample 410is placed in proximity to inductor 408. The best heating takes placewhen sample 410 is placed near the proximal (or “terminal”) end 411 ofinductor 408, and little or no heating occurs when sample 410 is placedat the distal (or “turn”) end 412 of inductor 408. Further, there is aheating gradient from terminal end 411 to turn end 412. In theory andwithout limitation, the best heating occurs at the terminal end 411because it is believed that the intensity of the electric fieldcomponent of the electromagnetic field at terminal end 411 is greaterthan at the distal end 412.

FIG. 5 illustrates a high level block diagram of another embodiment of aheating system 500 that is capable of generating an electromagneticfield for activating the compositions of the present invention. Heatingsystem 500 includes an alternating voltage generator 502 and a probe504, which is connected to an output terminal 501 of voltage generator502. Voltage generator 502 alternately positively charges and negativelycharges probe 504, thereby creating an electromagnetic field 506centered at probe 504. Heating can occur when sample 410 is placed inproximity to probe 504. How quickly and how much heating occurs dependson the sample itself, the strength of the electromagnetic field at thesample, and the frequency of the alternating voltage 509 produced byvoltage generator 502.

Generally, probe 504 is a conductive material, such as, but not limitedto copper, aluminum, or stainless steel. Generally, probe 504 can have avariety of shapes, including cylindrical, square, rectangular,triangular, etc. Preferably, probe 504 is square or rectangular. Probe504 can be hollow or solid, preferably hollow. Generally, probe 504 canbe straight or non-straight, such as curved. The preferredcharacteristics of probe 504 ultimately depends on the application thatit is being used for.

In yet another embodiment, which is illustrated in FIG. 6, heatingsystem 500 includes at least two probes 602 and 604 for activating thecompositions of the present invention. Probe 602 is connected to outputterminal 610, and probe 604 is connected to output terminal 612. Likeprobe 504, probes 602 and 604 are made from conductive materials asdiscussed above. Probes 602 and 604 can have a variety of shapes. Forexample, they can be either straight or curved. Preferably, at least aportion of probe 602 is parallel to a portion of probe 604, although nota required.

In the system shown in FIG. 6, probe 602 has a net positive charge whenprobe 604 has a net negative charge, and probe 602 has a net negativecharge when probe 604 has a net positive charge. When probes 602 and 604are oppositely charged, a strong electromagnetic field 606 is presentbetween the probes. Thus, sample 410 is preferably heated by placing itin a region above (or equivalently below) the region between probe 602and probe 604, as illustrated in FIG. 7A and 7B. This region is referredto as an activation region. Preferably, an insulating layer 702 (seeFIG. 7A) is placed between sample 410 and probes 602 and 604, althoughthis is not a requirement.

Generally, the vertical distance between sample 410 and probes 602 and604 ranges from about 0.01 to 2 inches, more preferably from about 0.02to 1 inch, and most preferably from about 0.025 to 0.185 inches. Sample410 can also be heated by placing it between probes 602 and 604.Generally, The center to center distance between probes 602 and 604ranges from about 0.1 to 3 inches, more preferably from about 0.2 to 2inches, and most preferably from about 0.25 to 0.75 inches.Additionally, in general, the height and width of a rectangular probe,or the diameter for a cylindrical probe, ranges between about 0.02 and0.5 inches, and the length generally ranges from about 0.25 inches to 20feet.

In one embodiment, the distal end 750 of probe 602 is curled to reducecorona effect (see FIG. 7C). For the same reason, the distal end ofprobe 604 is also curled.

An advantage that the two probe system shown in FIG. 6 has over thesystem shown in FIG. 4, is that sample 410 heats equally as welt at theproximal end of probes 602, 604 as it does at the distal end.Consequently, the system of FIG. 6 does not experience the heatinggradient problem that is encountered with the system of FIG. 4.

Generally, the compositions of the present invention may be activated bya frequency of the alternating voltage 509 ranging from about 1 KHz to 5GHz, more preferably from about 1 MHz to 80 MHz, and most preferablyfrom about 10 to 15 MHz. The peak to peak voltage between probes 602 and604 generally ranges from 1 to 15 kilo volts (kV). Generally, theduration of RF energy application to the sample 410 (also referred to asdwell time), for most applications, ranges from about 100 millisecondsto 30 seconds. However, there are some applications where the dwell timegreatly exceeds 30 seconds. In the case of a composition comprising athermoset resin, the dwell time ranges from about 1 second to 20minutes, preferably from about 1 to 10 minutes, and most preferably fromabout 2.5 to 5.0 minutes to initiate cross linking reactions(s) leadingto a high degree of thermoset character.

FIG. 8 illustrates one embodiment of alternating voltage supply 502. Theinvention, however, is not limited to this or any particular voltagesupply, since any system capable of generating a strong enoughelectromagnetic field could be utilized to activate the compositions ofthe present invention. In one embodiment, voltage supply 502 includesdirect current (DC) voltage source 802 that is connected to a broadbandamplifier 806 through DC power rail 804. The function of DC voltagesource 802 is to provide a DC voltage to broadband amplifier 806. The DCvoltage produced by DC voltage source 802 can range from 0 volts to 200volts. The magnitude of the voltage provided to broadband amplifier 806is dependent upon an output signal 815 from a main controller 814.Output signal 815 of main controller 814 can be controlled manually by auser 821 through user interface 820, or automatically by a productionline control system 822.

Broadband amplifier 806 amplifies a low level RF signal 817 generated byfrequency controller 816, and thus generates a high level RF powersignal 808. Preferably, the frequency of RF signal 817 ranges between 10MHz and 15 MHz. RF signal 808 is passed through a power sensor 810 andprovided to an impedance matching circuit 812 (also referred to hereinas “heat station”) through an RG393 50 ohm cable 811. Upon RF signal 808being inputted into impedance matching circuit 812, an electromagneticfield 606 is generated at the probes 602 and 604. This electromagneticfield is used to heat the compositions of the present invention.

While RF signal 808 is applied to impedance matching circuit 812, powersensor 810 continuously feeds a reflected power signal 832 to frequencycontroller 816 and main controller 814. Power sensor 810 alsocontinuously feeds a forward power signal to main controller 814.Reflected power signal 832 represents the amount of reflected power andforward power signal 830 represents the amount of forward power.

Frequency controller 816 uses reflected power signal 832 to continuallyadjust the frequency of RF signal 817 so as to minimize the amount ofreflected power. Main controller 814 uses forward power signal 830 andreflected power signal 832 to maintain the power level set by user 821through user interface 820 or set by production line control system 822.Main controller maintains the correct power level by adjusting the levelof DC voltage supplied by DC voltage source 802 and by adjusting theoutput level of RF signal 817 generated by frequency controller 816.

As sample 410 changes during a heating process, the impedance on theprobes 602 and 604 change, which causes a change in the forward andreflected power. Frequency controller 816 will detect this change inreflected power because it is receiving reflected power signal 832 frompower sensor 810. Frequency controller 816 changes the frequency of RFsignal 817 so as to minimize reflected power, thereby achieving anoptimum impedance match and insuring a repetitive power transfer fromheating system 800 to sample 410.

DC voltage source 802, sensor 810, frequency controller 416, and maincontroller 814 are further described in U.S. patent application Ser. No.09/113,518, entitled, “RF Power Supply,” which is incorporated herein byreference in its entirety. A broadband amplifier suitable for use inheating system 800 is described in U.S. patent application Ser. No.09/270,506, filed Mar. 17, 1999, entitled, “High Frequency PowerAmplifier,” which is incorporated in its entirety herein by reference.

FIG. 9 is a flow chart illustrating a process for heating a compositionaccording to the present invention using heating system 800. The processbegins with step 902 when user 821 or production line control system 822sends a “heat-on” signal to the main controller 814. Upon receiving the“heat-on” signal, main controller 814 begins an initial tuning processfor determining the frequency of RF signal 817 that produces the minimumamount of reflected power. The initial tuning process encompasses steps904-908. In step 904, main controller 814 directs DC voltage source 802to output a “tune” voltage. The “tune” voltage is the lowest voltagelevel that can provide a sufficient signal to measure the reflectedpower over a range of frequencies. The objective is to consume the leastamount of energy during the initial tuning process. Typically, the“tune” voltage level is 10% of the full scale voltage, where the fullscale voltage is the voltage at which the composition is intended to beheated.

After step 904, control passes to step 906. In step 906, heating system800 performs coarse tuning. That is, heating system 800 determines acoarse estimate (i.e., rough estimate) of the frequency that producesthe minimum reflected power. Hereafter this frequency shall be referredto as the resonant frequency. The coarse estimate of the resonantfrequency can be determined by sampling reflected power over a firstpredetermined frequency range. After step 906, control passes to step908. In step 908, the heating system 800 performs fine tuning. That is,the heating system 800 determines a fine estimate (i.e., more preciseestimate) of the resonant frequency. The fine estimate can be determinedby sampling the reflected power over a second frequency range, whichincludes the coarse estimate of the resonant frequency. After step 908,control passes to steps 910 and 912 in parallel. In step 910, maincontroller 814 ramps (i.e., rapidly increases) the voltage output by theDC voltage source 802 such that within approximately 30 milliseconds thevoltage increases from the “tuning” voltage level to approximately thefull scale voltage level. In step 912, the heating system 800continuously tracks the resonant frequency until a power of f indicationis received. The methods for coarse tuning, fine tuning, and trackingresonant frequency are described in U.S. patent application Ser. No.09/113,518.

FIG. 10A further illustrates one embodiment of impedance matchingcircuit 812. Impedance-matching circuit 812 is used to match theimpedance of 50 ohms on the input to the,variable impedance of theprobes 602 and 604 and sample 410. The impedance of the probes 602 and604 and sample 410 is typically in the order of 200 to 500 ohms. Theimpedance of the sample has an equivalent circuit of a resistancebetween 500 Ohms and 50 Kilo Ohms in parallel with a 0.1 picofaradcapacitor.

Circuit 812 includes a connector 1001, two capacitors 1002 and 1004, andan inductor 1006. Capacitor 1002 is a variable capacitor, which isadjustable from 10 to 50 picofarades (pf) to achieve impedance match tothe varying impedance of probes 602 and 604 and sample 410. Thecapacitance of capacitor 1004 is preferably 100 pf, and the inductanceof inductor 1006 is preferably 1.0 micro henries (μH). Capacitor 1004and inductor 1006 form a parallel resonance circuit that will resonatetypically at a frequency between 12.5 and 14.5 MHz. Capacitor 1004 andinductor 1006 are water cooled with a flow rate of approximately half agallon per minute. Probe 602 is connected to a node 1020 of circuit 812,and probe 604 is connected to a node 1022 of circuit 812. The high powerRF input 411 (typically less than 1 kilowatt) from a 50 ohm sourcegenerator is connected to connector 1001.

A process for setting the capacitance of variable capacitor 1002 willnow be described. The process begins by applying a low level RF signal(typically 10 watts) to input 1001 of circuit 812. The frequency of theapplied RF signal is adjusted until the amount of reflected power isminimized. The capacitance of capacitor 1002 is then adjusted tooptimize the reflected power minima. To achieve the least amount ofreflected power that is practical to achieve, which is about two percentreflected power (or 1.25 voltage standing wave ratio (VSWR)), thefrequency of the applied RF signal and the capacitance of capacitor 1002are adjusted in an iterative process. Once the process is completed,sample 410 is placed in proximity to probes 602 and 604. At this pointit may be necessary to adjust the frequency of operation and capacitor1002 in order to achieve an optimum reflected power. Once optimumreflected power is achieved, the power level of the input RF signal isincreased. As the input RF power level is increased the resonantfrequency of the matching circuit and probes 602 and 604 and sample 410will change requiring a change of operating frequency to continue tominimize the reflected power.

FIG. 10B illustrates another embodiment of impedance matching circuit812. In this embodiment, impedance matching circuit 812 includes aconnector 1051, a 1:1 balun transformer 1052, two variable capacitors1054 and 1056, and one inductor 1060. Capacitors 1054 and.1056 areadjustable from about 3 to 25 picofarades (pf) to achieve impedancematch to the varying impedance of probes 1082 and 1084 and sample 410.The inductance of inductor 1060 is preferably about 5 micro henries(mH). Capacitor 1058 is not an actual circuit element of the impedancematching circuit 812. Capacitor 1058 represents the capacitanceassociated with the inductor system, which consists of the inductor1060, the leads (not shown) connecting the inductor 1060 to thecapacitors 1054 and 1056, and the leads (not shown) connecting theprobes 1082 and 1084 to the inductor 1060. The capacitance of capacitor1058 is preferably less than about 15 pf. One advantage the impedancematching circuit 812 shown in FIG. 10B has over the impedance matchingcircuit shown in FIG. 10A, is that the impedance matching circuit 812shown in FIG. 10B provides a balanced signal on the probes 1082 and 1084relative to ground.

VII. Method of Bonding Substrates

The compositions of the present invention may be employed in a varietyof bonding methods, including but not limited to adhesive bonding,thermal bonding and mechanical bonding.

Adhesive bonding is accomplished when a susceptor composition isinterposed between two substrates that are to be joined (adherands) andactivated by RF energy to undergo adhesive attachment to each of theadherands.

In the case of thermoplastic adhesive compositions such as hot melts, RFenergy causes the composition to melt and wet-out onto adherands thatare in close contact. Upon cooling, the composition returns to a solidstate with sufficient cohesive strength and adhesion to each of theadherands to form a good bond. The degree of heating and melting of theadhesive composition is controlled by the intensity and duration of theapplied RF energy and the formulation of the adhesive composition. Suchcontrol is required to prevent undesired results stemming fromunder-heating or over-heating the adhesive composition. For example,under-heating can result in a weak bond due to insufficient wet-out ofthe adhesive onto the adherands. Also, over-heating can result inundesirable bond, with thermal distortion or destruction of theadherands, as well as thermal degradation of the thermoplasticcomposition.

In the case of thermoset adhesive compositions, RF energy causes thecomposition to become cured, resulting in sufficient increase incohesive strength and adhesion to adherands to form a strong bond. As inthe case of thermoplastic compositions, the degree of heating and curingof thermoset compositions is controlled by the intensity and duration ofthe applied RF energy. Such control is required to prevent undesiredresults from under-heating or over-heating. For example, under-heatingcan result in a weak bond due to insufficient cross-linking.Over-heating can cause effects such as thermal distortion or destructionof the adherands, as well as thermal degradation and excessive shrinkageof the thermosetting composition.

Thermal bonding is accomplished when the composition is used to generatesufficient heat to cause one or more adherands to become thermally fusedto each other.

One example of thermal bonding involves saturating a porousthermoplastic material, such as a non-woven polypropylene web, with anRF-heatable composition, and then interposing the saturated web ofmaterial between two adherands and RF-heating the composition to causethe saturated web and adjacent adherands to melt and fuse to each other.

Another example of thermal bonding involves saturating a porous, firstthermoplastic adherand with an RF-heatable composition, and then placingthe first adherand against a second thermoplastic adherand andRF-heating the composition to cause the first and second adherands tomelt and fuse together.

FIG. 11 shows a method of bonding polyolefin and non-polyolefinmaterials using a composition that is activated in the presence of RFenergy according to the present invention.

In step 1102, adherands that are to be bonded or adhered are chosen.Once the materials or layers are chosen, an appropriate composition isprepared in step 1104. For example, if nonwoven PP layers are chosen tobe bonded, a susceptor, which includes an ionomer as described herein,is combined with a polar carrier. The type of composition may depend onwhether a transparent, translucent, or lightly colored adhesive obtainedby the method of the present invention is needed for a particularapplication. After the composition is prepared in step 1104, control canpass to step 1106, 1109, or 1110.

In step 1106, a second carrier, such as an insoluble porous carrier(e.g., nonwoven PP), is saturated with the prepared composition. In step1108, the saturated insoluble porous carrier is then placed in betweenthe layers chosen to be bonded. RF energy is applied in step 1120. TheRF energy applied in step 1120 can be applied for 100 milliseconds toseveral minutes: The application of RF energy allows for the precisionheating of the layers to be bonded, without the unwanted side effects ofnon-uniform bonding, or damage to the bonded layers.

In step 1110, one or both of the layers to be bonded are coated with thecomposition. In step 1112, the composition is allowed to dry or the hotmelt to congeal depending on the type of composition created.Alternatively, a heat source (e.g. an oven or lamp) and fan may be usedto dry the coating or RF energy may be applied to drive of f any wateror other solvents. According to step 1114, the layers to be bonded areplaced together, such that the coated surfaces are in contact. Uniformpressure placed on the contacted layers helps enhance the bonding oradhesion process activated by the applied RF energy (step 1120). Suchuniform pressure may be applied while the composition is being activatedor immediately thereafter by use of conventional nip rollers.

In step 1109, a film of the composition is created. Such a film can becreated according to film making processes well known in the at. Thefilm made in step 1109 can then be sandwiched between the two materialsto be bonded in step 1111. RF power is then applied in accordance withstep 1120.

In a further embodiment, two or more adherands may be bonded or adheredby a process comprising: applying a first composition onto a firstadherand; applying a second composition onto a second adherand;contacting the first composition with the second composition; applyingRF energy to the first and second compositions to heat the compositions,thereby causing the first and second adherands to become adhered orbonded; wherein one of the compositions comprises a susceptor and theother of the susceptors is a polar carrier, and the susceptor and/or thecarrier are present in amounts effective to allow the first and secondcompositions to be heated by RF energy.

In this embodiment of the invention, the susceptor and carriercomponents of the composition are applied separately to the adherandsprior to placing the adherands together. FIG. 52 shows asusceptor-coated adherand 5201 assembled to an adherand 5203 coated withthe polar carrier. After coating one or both of the adherands, one mayapply a temporary release liner 5205 to the coated side to allow thecoated adherand to be rolled up or stacked. Alternatively, one may dryone or both coatings.

After nipping the two coated adherands in the assembly stage, theassembly is passed through an RF field 5207 for activation. The RFenergy causes the susceptor and carrier to heat with the resultingadhesion between the two adherands. The final nip rollers 5209 press andbonds the two adherands, while cooling the bond line.

FIG. 53 shows the replacement of the pre-applied polar carrier on theadherand with a polar carrier spray coated onto the adherand just priorto the assembly nip rollers 5206. A polar carrier is applied (e.g.sprayed or otherwise as described herein) by a spray applicator 5302onto adherand 5201. When assembled with the susceptor coated adherand5203 and exposed to RF energy, the interfaced composition activates toform a bond.

VIII. Additional Probe Embodiments

additional embodiments of probes 602 and 604 are described below withreference to FIGS. 12 to 17. These additional embodiments are in no waylimiting and merely provide additional examples of possibleconfigurations of the probes.

In FIG. 12, probes 602 and 604 are each curvilinear and oppositelycharged. In this particular example, probes 602 and 604 are sinusoidallyor “S” shaped, but any similar arrangement is possible. Probes 602 and604 are made from conductive materials, as described above, preferably,but not limited to, copper, aluminum, or stainless steel. Probe 602includes a proximal region 1206, and activation region 1208 and a distalregion 1210. Similarly, probe 604 includes a proximal region 1212, anactivation region 1214, and a distal region 1216. In proximal regions1206 and 1212, probes 602 and 604 are spaced apart in order to preventarcing. The amount of spacing depends on the size of probes 602 and 604,and in one example, probes of 0.125 inch square cross-section should bespaced at least 1.1875 inches apart. Similarly, distal regions 1210 and1216 are spaced apart to prevent arcing, the amount of such spacing issimilarly dependent upon the size of the probes. In activation regions1208 and 1214, probes 602 and 604 are in proximity to one another inorder to create an electromagnetic field between the probes. How closeprobes 602 and 604 must be to one another again depends on the size ofthe probes and the magnitude of the charge on them. In one example,probes 602 and 604 have about a 0.125 inch square cross-section andpreferably spaced between 0.25 and 0.75 inches apart. It is preferablethe space between probes 602 and 604 remains substantially equalthroughout the activation region, but it is not necessary. An activationzone 1222 is defined in activation regions 1208 and 1214 between anoutermost end 1218 of probe 602 and an outermost end 1220 of probe 604.Activation zone 1222 is indicated in dashed lines in FIG. 12. Activationzone 1222 defines the area of sample 410 that can be heated/activated bythe system when the substrates being joined are moving in the directionindicated. If the substrates are stationary with respect to the probes,the activation zone is defined by the area in between the probes.

In another embodiment, probes 602 and 604 may be repeated in order toprovide a larger activation zone. Such an arrangement is shown in FIGS.13A, 13B and 13C. For example, in FIG. 13A, a pattern of one probe 602and two probes 604 is provided. This arrangement may include any numberof probes 602 and 604, as long as oppositely charged probes are placednext to one another. This arrangement works equally well with multiplesets of curvilinear probes, as shown in FIG. 13B.

FIG. 13C illustrates one embodiment of what is termed an “interdigitatedprobe system.” The interdigitated probe system 1301 is advantageousbecause it provides an extended activation zone, as shown by the dottedrectangle 1350. Interdigitated probe system 1301 includes a firstelement 1302 and a second element 1304.

The first element 1302 includes a first conductor 1310 and one or moresecond conductors 1322 connected to the first conductor 1310.Preferably, conductors 1322 are coplanar and uniformly spaced apart, butthis is not a requirement. Additionally, in one configuration of element1302, each conductor 1322 forms a right angle with conductor 1310, butthis is also not a requirement.

Similarly, the second element 1304 includes a first conductor 1312 andone or more second conductors 1320 connected to the first conductor1312. Preferably, conductors 1320 are coplanar and uniformly spacedapart, but this is not a requirement. Additionally, in one configurationof element 1304, each conductor 1320 forms a right angle with conductor1312, but this is also not a requirement.

In one embodiment, first element 1302 and second element 1304 areorientated such that conductors 1320 are coplanar with conductors 1322and each conductor 1320 is adjacent to at least one conductor 1322.First element 1302 and second element 1304 are not limited to anyparticular type of conductive material. However, conductors 1310, 1312,1320, and 1322 are preferably copper, and more particularly, coppertubes. In one embodiment, the copper tubes have a one-eighth of an inchdiameter.

In one embodiment, the length of conductors 1310 and 1312 is about 40inches, and the length of conductors 1320 and 1322 is about 2 inches.However, conductors 1310, 1312, 1320, and 1322 are not limited to anyparticular length. Typically, the length of conductors 1310 and 1312ranges between about 3 inches and 80 inches, and the length ofconductors 1320 and 1322 ranges between about 1 inch and 70 inches.

FIG. 14 shows another embodiment of a probe system for activating amulti-sided sample 1402. In this embodiment, sample 1402 is mounted on ablock 1404. Sample 1402 may be mounted on any similar device whichallows each side of sample 1402 to be exposed to moving probe blocks1406. This particular example shows a three-sided sample exposed tothree moving probe blocks 1406, however, the sample may include moresides and be exposed to an equivalent amount of moving probe blocks.Probe blocks 1406 include probes 602 and 604 mounted in an electricallyinsulating material such as, but not limited to, polytetrafluoroethylene(TEFLON™). Probes 602 and 604 are mounted on pressure plates 1408 ofprobe blocks 1406. In this particular example, three probes are used ineach probe block 1406, two negatively charged probes 604 and onepositively charged probe 602. However, more or less probes can be used,depending on the size of the probe blocks, as long as adjacent probesare oppositely charged. Probes 602 and 604 are coupled to an alternatingvoltage supply 502, via output terminals 610 and 612 as generally shownin FIG. 6. Probe blocks 1406 are moved into proximity of sample 1402mounted on block 1404, preferably between 0.125 and 0.375 inch, therebyactivating the compositions of the present invention, as previouslydescribed. Alternatively, probe blocks 1406 could be placed at theappropriate interval and block 1404 with sample 1402 could be moved intoposition to be activated. While FIG. 14 shows the probe blocks 1406 ashaving a regular shape, one skilled in the art will recognize that theprobe blocks could be any three dimensional shaped object.

FIG. 15 shows another embodiment for activating a multi-sided sample1502 using a stationary probe system. In this embodiment, probes 602 and604 are mounted on multiple sides of a single probe block 1504, similarto the manner in which probes 602 and 604 were mounted in probe blocks1406, described above. In this particular example, probes 602 aremounted on three sides of a generally square probe block 1504, butprobes 602 and 604 could be mounted on multiple sides of any polygonalblock or three dimensional object. Sample 1502 is brought into proximityof probe block 1504 by pressure plates 1506, thereby activating thecompositions of the present invention, as previously described. In thisparticular example, two negatively charged probes 604 and one positivelycharged probe 602 are shown on each side of probe block 1504, however,it will be recognized that any number of probes could be utilized,depending on the application, as long as adjacent probes are oppositelycharged. Probes 602 and 604 are coupled to an alternating voltage source502 via output terminals 610 and 612, as generally depicted in FIG. 6.

FIGS. 16A and 16B show yet another embodiment of a probe system foractivating a sample material including compositions of the presentinvention. In FIGS. 16A and 16B, sample 1602 is draped over a conveyorrod 1604 and generally moves along the circumference of the conveyorrod. Conveyor rod 1604 is constructed of electrically non-conductivematerial. A probe system 1606 is disposed in proximity to a portion ofthe circumference of conveyor rod 1604, e.g., 0.02 to 1.5 inches, andmore preferably within 0.125 to 0.375 inch, and is shaped to conform tothe shape of conveyor rod 1604, as best seen in FIG. 16B. Probe system1606 includes adjacent alternately charged probes 602 and 604 foractivating sample 1602. Probes 602 and 604 are coupled to an alternatingvoltage source 502, as generally depicted in FIG. 6.

The probe systems described above all activate a single side of thesample material. However, probe systems could be placed on both sides ofthe material in each of the above-described embodiments, provided thatthe polarity of the probes is such that the electromagnetic fields donot cancel each other out. A particular example of an activation systemfor activating both sides of the material is shown in FIG. 17. Ratherthan using a probe system, two oppositely charged conductive plates 1702(positively charge) and 1704 (negatively charged) are disposed onopposite sides of sample material 1706. Plates 1702 and 1704 arepreferably constructed of copper, but may be constructed of any suitableconductive material, such as the aforementioned conductive materials ofprobes 602 and 604. Sample material 1706 may be stationary or movingwhen exposed to the activation region between plates 1702 and 1704.Plates 1702 and 1704 are preferably spaced between 0.02 and 24 inches,more preferably between 0.02 and 15 inches, and most preferably between0.05 and 0.375 inches. Plates 1702 and 1704 are coupled to analternating voltage source 502 via output terminals 610 and 612, asgenerally depicted in FIG. 6.

IX. Applicator System for Applying a Composition of the PresentInvention to a Substrate/Adherand

FIG. 18 illustrates one embodiment of an application system 1800 forapplying a composition according to the present invention to an adherand1810. The manufacturing system includes an applicator 1815. Applicator1815 applies a hot melt or liquid dispersion or powder of thecomposition 1812 to one side of adherand 1810. Composition 1812 may beapplied via a hot melt by applying heat to the composition 1812 so thatit reaches its melting point and can be applied to an adherand. In a hotmelt application heat is applied to the composition 1812 in theapplicator 1815, and the composition 1812 is applied to the adherand ata temperature between 200 and 325 degrees Fahrenheit, preferably 250degrees Fahrenheit.

Composition 1812 may also be formulated as a liquid dispersion. Thecomposition 1812 can then be applied to the adherand at roomtemperature. Once the liquid dispersion composition 1812 is applied tothe adherand, the coated material 1810 is passed through a heatingsystem 1820. Heating system 1820 acts to dry the composition 1812.Heating system 1820 can be any conventional heating system, like anoven, or heating system 1820 can be an RF heating system, such asheating system 500 described above. Other drying means that may beemployed include, for example, a heat lamp with or without a fan toremove volatiles, or microwave heating system.

Composition 1812 can be applied in powder form by conventionalelectrostatic gun/spray.

In one embodiment, the coated adherand 1810 is rolled onto a roller 1830after composition. 1812 is sufficiently dried. Alternatively, the coatedadherand 1810 can be cut into pieces and stacked. The coated susceptor1810 can be used at a later point in time in the bonding processdescribed above. The bonding process can occur anytime within a fewseconds up to many months after the adherand 1810 has been coated withcomposition 1812.

X. Systems for Adhering or Bonding Two Adherands.

FIG. 19 illustrates one embodiment of a system for bonding or adheringvarious adherands or layers. The system utilizes RF heating system 400,including power supply 402, cable 404, heat station 406, and coil 408,and clamp 1902. The adherands to be bonded by RF heating 400, shown aslayers 1910, pass through or in proximity to coil 408. Layers 1910 caneither be coated with a suitable susceptor composition, can sandwich afilm made from a susceptor composition or can sandwich an insoluble,porous carrier (such as a thermoplastic carrier web) that is saturatedwith a susceptor composition as described above. A clamp 1902 providesuniform pressure to the adherands to be bonded or adhered.Alternatively, coil 408 can be implemented to provide a uniform pressureto the adherands to be bonded or adhered. Precision bonding or adheringtakes place as the layers 1910 are exposed to the electromagnetic fieldgenerated when an alternating current flows through coil 408. Theelectromagnetic field has sufficient RF energy to activate the bondingcomposition. Preferably, layers 1910 are exposed to the electromagneticfield for at least 100 milliseconds to several seconds or minutes. Inthe case of thermoset compositions, in general, longer times are needed,e.g. from 1 second to several minutes or hours.

FIGS. 20A and 20B illustrates a static bonding system 2000 for bondingor adhering adherands 2090 and 2092 (see FIG. 20B). Bonding system 2000is referred to as a static because the adherands to be bonded do notsubstantially move while they are being exposed to the electromagneticfield that activates an RF activatable composition which is locatedbetween the adherands.

Referring now to FIG. 20A, bonding system 2000 includes a power supply,such as voltage supply 502, for generating an alternating voltagebetween output terminal 612 and output terminal 610. Connected to outputterminal 612 is a probe 2006, and connected to output terminal 610 is aprobe 2008. The characteristics of probe 2006 and probe 2008 aredescribed above with reference to probes 602 and 604. In one embodiment,probe 2006 and 2008 are rectangular hollow tubes made from a conductivematerial, preferably copper. Preferably, the height (H) and width (W) ofeach probe is about equal, and the length (L) is generally larger thanthe height and width. For example, in one embodiment, the height andwidth of each probe is about, ⅛ of an inch, whereas the length of eachprobe is about 10 inches. In general, the height and width of arectangular probe, or the diameter for a cylindrical probe, rangesbetween about 0.02 and 0.5 inches, and the length generally ranges fromabout 0.25 inches to 20 feet.

System 2000 is not limited to two probes. A third probe (not shown)could be placed adjacent to probe 2006 such that probe 2006 will then bebetween the new probe and probe 2008. With this configuration, the newprobe would be connected to the output terminal that probe 2008 isconnected to, which in this case is terminal 610. An exemplary threeprobed system is illustrated in FIG. 13A. One skilled in the art shouldrecognize that any number of probes could be used, provided that no twoadjacent probes are connected to the same output terminal of voltagesupply 502.

In one embodiment, probes 2006 and 2008 are placed in an electricallyinsulating block 2010. Insulating block 2010 is composed of anelectrically insulating material, such as, but not limited topolytetrafluoroethylene (TEFLON™). An optional electrically insulatinglayer 2012 (see FIG. 20B) may be placed on top of probes 2006 and 2008.Preferably, electrically insulating layer is made frompolytetrafluoroethylene or other like material which resists adhesion ofthe substrates or adherands thereto.

An alternative electrically insulating block 2050 is illustrated in FIG.20C. FIG. 20C shows a cross-sectional view of probes 2006 and 2008housed within the insulating block 2050. Insulating block 2050 is formedfrom two elements, insulating element 2052 and insulating element 2054.

Insulating element 2052 has two U shaped recesses 2056 and 2058 forreceiving probes 2006 and 2008, respectively. In one embodiment, a lowdielectric encapsulate 2060 is placed with the probes in the recesses.Insulating element 2054 has two protrusions 2062 and 2064 for matingwith the recesses 2056 and 2058 of insulating element 2052. Preferably,both insulating element 2052 and insulating element 2054 consistprimarily of polytetrafluoroethylene (TEFLON™).

Referring now to FIG. 20B, to bond adherand 2090 to adherand 2092,adherand 2090 and/or adherand 2092 is coated with a suitable composition2091, or a film of the composition 2091 is sandwiched between adherand2090 and adherand 2092, or an insoluble porous carrier is saturated withcomposition 2091 and placed between adherand 2090 and adherand 2092.Adherands 2090 and 2092 are then placed over probes 2006 and 2008 suchthat composition 2091 is between the adherands and over the regionbetween probe 2006 and probe 2008, as shown. Power supply 502 is thenactivated, which creates an alternating voltage between terminals 612and 610, which creates an electromagnetic field between probes 2006 and2008. The composition 2091 is exposed to the electromagnetic field for apredetermined amount of time. The predetermined amount of time can rangebetween about 100 milliseconds to about one second, several minutes, orhours depending on the composition and/or the strength of theelectromagnetic field. The electromagnetic field causes composition 2091to heat. When composition 2091 reaches a given temperature, thecomposition will begin to melt and flow, causing an impedance change onthe matching circuit 812. The impedance change can be detected by achange in reflected power signal 832. This change in reflected powersignal 832 can be used to control the intensity of the RF energy. Othermethods of detecting when composition 2091 melts is to detectdisplacement of a pressure plate 2020 with a feed back loop. After thepredetermined amount of time has expired or while the composition isexposed to 155 the electromagnetic field, the adherand can be pressedtogether using pressure plate 2020, pressure roller (not shown), or anyother pressure delivery apparatus or means, thereby assuring a goodbond.

The resulting bond can be an adhesive bond, mechanical bond, thermalbond, or any combination of aforementioned bonds. For example,composition 2091 may have adhesive properties to create an adhesive bondbetween adherands 2090 and 2092, and/or composition 2091 may be used asa source of thermal energy for welding the adherands together.

An advantage of the present invention is that non-electricallyconductive materials can be stacked on top of an adherand withoutaffecting the bonding process. Only composition 2091 is directly heatedwhen the layers are exposed to RF energy having the preferred frequencyrange of 10 to 15 MHz. Thus, by selectively heating only the composition2091, multiple layers may be assembled prior to forming the bond betweenadherands 2090 and 2092. This allows the assembly of complex laminatesprior to bonding.

Another advantage of the present invention is that RF energy can bereapplied to the bonded product and the two (or more) adherands 2090 and2092 can be disassembled. This is known as de-activating the composition2091. In fact, the composition 2091 can be activated and de-activated anumber of times.

FIGS. 38 and 39 illustrate two exemplary manufacturing systems in whichstatic bonding system 2000 could be utilized. FIG. 38 illustrates a stepand repeat manufacturing system. There are many applications in generalmanufacturing where adherands are joined or bonded together using anadhesive. In a conventional step and repeat joining (or bonding) systemthere is a gluing station immediately followed by a joining station. Thegluing station applies an adhesive to an adherand. After the adhesive isapplied, the adherand moves immediately to a joining station where it isbrought together with the other adherand to which it is to be joined.The joining station then nips the adherands together to form a bond.

The adhesive compositions according to the present invention allow theadhesive to be applied to the adherand(s) prior to the adherand(s)entering the manufacturing line. For example, the adhesive compositionsaccording to the present invention may be applied at the part supplier'sfacility with on-demand bonding occurring for, example, days, weeks, ormonths later, by RF activation.

Referring now to FIG. 38, a step and repeat manufacturing process asapplied to a continuous production line 3802 with base adherand 3806 andtop adherand 3808 being supplied to bonding system 2000 on a conveyorsystem 3804. In one embodiment, base adherand 3806 is pre-coated with anadhesive composition 3805 according to the present invention. Baseadherand 3806 could have been coated minutes, days, weeks, or monthsprior to base adherand 3806 entering continuous production line 3802.Base adherand 3806 travels along the conveyor 3804 and top adherand 3808is assembled to base adherand 3806 by hand or automatic system (notshown). The assembled adherands 3810 are placed onto a pressure plate2010 in which probes 2006 and 2008 are embedded. The bonding processbegins when an electromagnetic field is created between probes 2006 and2008 by power supply 502. The electromagnetic field activates theadhesive composition 3805, which then creates a bond between adherands3806 and 3808. Pressure plate 2020 is used to nip the bond during and/orafter RF activation. After the bond is nipped, the assembly 3810 isremoved from bonding system 2000 and placed back on the conveyor 3804.

FIG. 39 illustrates an index table bonding system. Index table bondingsystems are used in many manufacturing industries to automate thebonding process. Examples include the bonding of labels onto bottles.The index table process allows for setting up multiple stations wheredifferent processes in the assembly process are performed. The time theindex table stops at each station is the same, thus it is dependent uponthe slowest process. An advantage of using an adhesive compositionaccording to the present invention includes the pre-application to oneor both of the parts to be bonded prior to loading the parts onto theindex table. Other advantages are fast activation and curing time.Consequently, by removing the adhesive application from the index table,one less station is used and a higher production throughput is achieved.

Referring now to FIG. 39, an index table bonding system is described.The index table bonding system includes an index table 3902, which isgenerally round and rotates either clockwise or counter-clockwise. Baseparts 3904(1)-(N) having a pre-applied adhesive composition 3906 areplaced onto index table 3902. When index table 3902 moves base part3904(1) to the next station (station 2), a top part. 3908 is placed ontobase part 3904 to form assembly 3910. Assembly 3910 then moves tostation 3 where it is exposed to an RF field, which activates adhesivecomposition 3906. In station 3, the RF field is generated by probes (notshown) positioned so that adhesive composition 3906 is activated. Theprobes may be configured to either contact the assembly 3910 and applysome pressure to aid in the bonding process. Alternatively, the probescould be configured so there is no contact with the assembly 3910. Afteractivation of the adhesive 3906, the assembly 3910 moves to station 4for a nip or cure portion of the bonding process. After station 4, theassembly 3909 moves to station 5 where it is unloaded from the indextable 3902.

FIG. 21 illustrates a dynamic bonding system 2100 (also referred to asan in-line bonding system) for bonding or adhering adherands. Bondingsystem 2100 is referred to as dynamic because the adherands to beadhered, adherands 2110 and 2112, continuously move through anelectromagnetic field; which is generated by heating system 2140. In oneembodiment, adherand 2110 is pre-coated with a composition 2104according to the system shown in FIG. 18.

Bonding system 2100 includes a roll 2102 of coated adherand 2110 andplurality of rollers 2120, 2122, 2124, 2126, and 2128 for, among otherthings, continuously guiding coated adherand 2110 and adherand 2112through an electromagnetic field generated by heating system 2140. Inone embodiment, coated adherand 2110 and adherand 2112 move through theelectromagnetic field at a rate of about 0.01 to 2000 feet per minute,most preferably, about 1000 feet per minute (ft/minute).

The bonding process begins when coated adherand 2110 is fed onto roller2120. Coated adherand 2110 is then passed over roller 2122. A pressureactivated construction bond may be formed by passing the two adherands2110 and 2112 between roller 2122 and nip roller 2124. A constructionbond may be required in this process to maintain the proper location ofcoated adherand 2110 and adherand 2112 prior to and/or duringactivation. Preferably, the composition 2104 is formulated to provide apressure sensitive tack when a construction bond is needed. Coatedadherand 2110 and adherand 2112 are not limited to any particularthickness. As should be readily apparent to one skilled in the art, thesystem can be designed to accommodate any reasonable thickness ofadherand.

In this embodiment, the invention relates to a method for dynamicallybonding a first adherand to a second adherand, comprising:

(1) creating an article of manufacture comprising the first adherand,the second adherand, and a composition, the composition being placedbetween the first adherand and the second adherand, wherein thecomposition can be activated in the presence of an RF field;

(2) moving the article of manufacture along a predetermined path;

(3) generating along a portion of the predetermined path an RF fieldhaving sufficient energy to activate the composition, wherein thecomposition is activated by its less than one second exposure to the RFfield.

In a preferred embodiment, the article passes through the RF field at arate of at least about one-thousand feet per minute. In a more preferredembodiment, the article passes through the RF field at a rate of about1000 feet per minute.

Referring now to FIG. 22, after the construction bond is formed, theconstruction bonded coated adherand 2110 and adherand 2112 are passedthrough an RF field 2230, which is generated by heating system 2140.FIG. 22 further illustrates heating system 2140 for use in dynamicbonding system 2100.

Heating system 2140 includes a power supply, such as power supply 502,for generating an alternating voltage between terminal 612 and terminal610. Connected to terminal 612 is a probe 2210, and connected toterminal 610 is a probe 2220. The characteristics of probes 2210 and2220 are described above with reference to probes 602 and 604 and probes2006 and 2008. In one embodiment, probe 2210 has a distal section 2211,a center section 2212 and a proximal section 2213. Similarly, in oneembodiment probe 2220 has a distal section 2221, a center section 2222and a proximal section 2223. Preferably, center section 2212 is parallelwith center section 2222, and they both have a length of about 48 incheswhen the adherands 2110 and 2112 are traveling at about 1000 feet/minutein the direction indicated by arrow 2130. This configuration results inabout a preferred 240 millisecond dwell time. Dwell time refers to themaximum amount of time that any given point on adherands 2110 and 2112is positioned beneath (or over) probes 2210 and 2220 (i.e., within theactivation region). If the speed of the adherands 2110 and 2112 isincreased, the preferred dwell time can remain constant by increasingthe length of probes 2210 and 2212. For example, if it is desired forthe adherands 2110 and 2112 to move at a rate of about 2000 feet/minover probes 2210 and 2220, and the preferred dwell time is about 100milliseconds, then the minimum length of probes 2210 and 2220 would beabout 40 inches. Although a preferred dwell time is 600 milliseconds,the dwell time can be increased to several minutes if desired byincreasing the length of probes 2210 and 2220, e.g., from about the 20inches to 20 feet, and/or decreasing the speed at which adherands 2112and 2110 travel over probes 2210 and 2220. Shorter probes are alsocontemplated, for example from about 0.25 inches to about 20 inches.

Preferably, probes 2210 and 2220 are positioned with respect to coatedadherand 2110 such that the composition that coats coated adherand 2110is beneath (or above) an activation region. The activation region is thearea between the center section 2212 and center section 2222.

The frequency of the alternating voltage generated by power supply 502can range from the low Kilohertz to high Gigahertz range. In oneembodiment the frequency ranges between about 1 MHz to about 5 GHz, mostpreferably about 10 MHz and 15 MHz. The peak to peak level of thevoltage generated by power supply 502 may range from about 500 V to 20kV, most preferably about 1 to 15 kV. The composition 2104 will remainactivated as long as the RF energy is delivered.

After the adherands 2110 and 2112 pass over (or under) probes 2210 and2220 they are nipped by non-destructive nip rollers 2126 and 2128, whichassure that a good bond is created between adherand 2110 and adherand2112. For optimal performance, the nip rollers 2126 and 2128 applypressure immediately after re-flow temperatures are achieved within theadhesive material additionally, nip roller 2126 and/or nip roller 2128may be cooled to remove thermal energy from the adherands. Upon cooling,the composition forms a strong bond between the adherands 2110 and 2112.The bonded adherands can then be subsequently processed in accordancewith a particular application.

There are a number of benefits of the above system. First, the systemprovides a finished bond in less than about one second of activation.Second, the activation process does not produce harmful emissions orby-products that may interfere with the bonding of two thin films.Third, the activation only occurs in the activation region.

FIGS. 23-27 illustrate alternative designs for heating system 2140. Asshown in FIG. 23, curved probes 2310 and 2320 can be used in place ofstraight probes 2210 and 2220. An advantage of curved probes 2310 and2320 is that the width 2390 of the activation region is greater then thedistance 2311 between probes 2310 and 2320, whereas the width of theactivation region provided by probes 2210 and 2220 equals the distancebetween center section 2212 of probe 2210 and center section 2222 ofprobe 2220.

The heating system shown in FIG. 24 includes probe 2410 in addition toprobes 2210 and 2220. Probe 2410 is positioned between probes 2210 and2220. Probe 2410 is parallel with probes 2210 and 2220. Preferably, thedistance (d) between probe 2410 and 2210 is equal to the distance (d)between probe 2410 and probe 2220. Probes 2210 and 2220 are bothconnected to the same output terminal of voltage supply 502, whereasprobe 2410 is connected to the other output terminal. An advantage ofthe probe design illustrated in FIG. 24, is that it provides a largeractivation region. The width 2420 of the activation region is greaterthan the distance (d) between any two of the probes. Based on the abovedescription, one skilled in the art will recognize that any number ofprobes can be used in heating system 2140, provided that no two adjacentprobes are connected to the same output terminal of voltage supply 502.

The heating system shown in FIG. 25 is similar in concept to the oneshown in FIG. 24. A curved probe 2510 is placed between curved probes2310 and 2320. Curved probes 2310 and 2320 are both connected to thesame output terminal of voltage supply 502, whereas probe 2510 isconnected to the other output terminal. Again, an advantage of theheating system shown in FIG. 25 is that it can provide a largeractivation region than the similar heating system shown in FIG. 23.

FIG. 26 illustrates another heating system. The heating system shown inFIG. 26 includes two plates 2610 and 2620. Plate 2610 is positionedabove adherand 2110 and plate 2620 is positioned below adherand 2112.Thus, composition 2104 travels between plates 2610 and 2620. Plate 2610is connected to output terminal 610 of voltage supply 502, and plate2620 is connected to output terminal 612 of voltage supply 502. Whenvoltage supply 502 is turned on, it generates an electromagnetic fieldbetween plates 2610 and 2620, which is used to activate composition2104. FIG. 27 illustrates another perspective of plates 2610 and 2620.As is apparent from FIG. 27, the width of the activation region for thisdesign is simply the width (W) of the plates. The center to centerdistance (d) between plate 2610 and plate 2620 can range from 0.02inches to 20 inches. In one embodiment, the distance ranges between 0.25inches and 1.5 inches. The length (L) of course depends on the desireddwell time and the rate at which any given point on adherand 2110 or2112 travels between any two points along the length of one of theplates.

XI. Exemplary Specific Applications of the Present Invention

The susceptor compositions may be employed for many purposes includingbonding, cutting, and coating. Thus, the susceptor compositions may beemployed for packaging applications, e.g. to bond or adhere cases orcartons as described in U.S. Pat. No. 5,018,337, but with the additionalstep of RF activation. Applications for the RF cured thermosetcompositions, which are illustrative only arid not to be consideredlimiting of the scope of the present invention, include:

Coatings for conventional and spray applications on plastics, metals,wood etc.

Corrosion resistance coatings.

Industrial and protective coatings.

Top coats.

Automotive coatings.

Lamination of composites.

Laminating adhesives.

Bonding of structural composites.

Inks and decorative coatings.

Barrier coatings.

Additional applications are listed below, but are likewise illustrativeand not limiting of the scope of the present invention.

A. Manufacture of Flexible Packaging

FIGS. 28A and 28B illustrate one embodiment of a system for themanufacture of flexible packaging. Flexible packages are used for, amongother things, packaging foods. The system includes a system 2802 (seeFIG. 28A) for manufacturing an RF activated adhesive film 2815 and abonding system 2804 (see FIG. 28B) for bonding the adhesive film 2815 toanother film 2850.

Referring now to FIG. 28A, film manufacturing system 2802 includes anextruding system 2810, a casting wheel 2814 a heating system 2820, astretching system 2830, and an optional film roller 2840. In oneembodiment, extruding system 2810 includes three extruders 2811, 2812,and 2813. An RF activated adhesive composition according to the presentinvention is first formulated into an extrudable resin (for example,ethylene vinyl acetate or other polymer based material is added to theadhesive composition) and then provided to extruder 2813 in a pellet orliquid form. Polypropylene or other like similar substance, such as butnot limited to ethylene vinyl acetate (EVA), is provided to extruder2811, and a sealing material is provided to extruder 2812. The output ofextruders 2811-2813 are cast into a film 2815 by casting wheel 2814.

FIG. 29 illustrates film 2815. As shown in FIG. 29, film 2815 includes afirst layer 2902 consisting of the sealing material, a second layer2904, e.g., OPP and/or EVA and/or other similar substance, and a thirdlayer 2906 consisting of the RF activated adhesive. Because film 2815includes an adhesive composition according to the present invention,film 2815 can be RF activated.

Referring back to FIG. 28A, film 2815 is provided to heating system2820. In one embodiment, heating system 2820 includes heater rollers2821 and 2822. The function of heating system is to heat the film to atemperature that allows the film to be stretched. After being processedby heating system 2820, film 2815 is stretched by stretching system2830. In one embodiment, stretching system 2830 includes a plurality ofstretch rollers 2831, 2832, 2833, 2834, and 2835 and a transversestretcher 2837. Stretching system 2830 stretches film 2815 both lengthand width wise. After being stretched, film 2815 may be rolled up usingfilm roller 2840. Alternatively, film 2815 can be cut and stacked afterbeing stretched.

Referring now to FIG. 28B, bonding system 2804 is used to bond film 2815with film 2850. In one embodiment, film 2850 is a 70 gauge orientedpolypropylene (OPP) film. Film 2850 is passed over a print wheel 2855and then through oven 2857. A pair of nip rollers 2860 and 2861 pressfilm 2815 with film 2850 to form a construction bond and thus form asingle multi-layer film 2870. FIG. 30 illustrates one embodiment of film2870.

As shown in FIG. 30, film 2870 includes layer 2902 consisting of thesealing material, layer 2904 that includes thermoplastics and/orelastomers, for example, OPP and/or EVA and/or other similar substance,third layer 2906 consisting of the RF activated adhesive, a fourth layer3002 consisting of the ink applied by print wheel 2855, and a fifthlayer 3004 consisting of film 2850.

Referring back to FIG. 28B, an RF heating system 2875 creates an RFfield that is used to heat adhesive layer 2906. Heating system 2875defines an activation region. The activation region is an area in whichthe RF field generated by heating system 2875 is strong enough toactivate adhesive layer 2906. Film 2870 can travel through theactivation region in as quickly as about 100 milliseconds.. Shortlyafter passing through the activation region, film 2870 is nipped by niprollers 2880 and 2881 and then rolled by film roller 2885. FIGS. 16A and16B illustrate one embodiment of the probe portion of heating system2875. Other heating systems could be used, such as those described abovewith respect to FIGS. 20 and 21.

FIG. 31 illustrates an alternative system 3100 for manufacturing an RFactivated adhesive film for use in the flexible packaging industry.System 3100 is similar to system 2802, except that system 3100 does notinclude extruder 2813. In place of extruder 2813, system 3100 includesan adhesive applicator 3101 and a heating system 3102. An adhesivecomposition according to the present invention is formulated into aliquid dispersion and applied to film 2815 by adhesive applicator 3101.In one embodiment adhesive applicator 3101 includes a gravureapplication tool (not shown). Heating system 3102 can be a conventionalheating system, such as an oven, or it can be an RF heating system, suchas heating system 600 or any of the other heating systems describedherein.

B. Food Packaging and Cap Sealing

Conventionally, metallic foils are used as susceptors of electromagneticenergy to generate heat for package sealing. Typical examples includetamper evident bottle seals (i.e., cap sealing) and food packaging.While the conventional systems are effective in sealing the packages,the use of metallic foils eliminates the manufacturer's ability toperform post sealing inspection, such as metal detection, x-ray, and thelike. Additionally, there may be a recycling benefit and a cost savingto the system by eliminating the metallic foil.

One solution is to replace the metallic foil with a composition of thepresent invention. The composition may or may not have adhesiveproperties. FIG. 32 illustrates a conventional aseptic packageconstruction. A conventional aseptic package includes an outerpolyethylene layer 3202, a paper layer 3204, a second polyethylene layer3206, a layer of metallic foil 3208, a third 3210 polyethylene layer, aninner polyethylene layer 3212, and a container 3214 that holds the foodor beverage. Inner polyethylene layer 3212 is the layer that contactswith the container 3214, and is used to seal the container during thefood packaging process. The sealing is achieved through inductionheating of the metallic foil layer 3208 causing the inner polypropylenelayer 3212 to melt and bond to the container 3214.

FIG. 33 illustrates one embodiment of a packaging construction that doesnot use metallic foils. The packaging construction includes the outerpolyethylene layer 3202, the paper layer 3204, the second polyethylenelayer 3206, a susceptor composition according to the present invention3302, a barrier layer 3310, an inner layer 3212, and a container 3214that holds the food or beverage. Inner layer 3212 is the layer thatcontacts with the container 3214, and is used to seal the container 3214during the food packaging process. Inner layer 3212 can be apolyethylene or EVA layer. In one embodiment, barrier layer 3310 is anEVOH barrier layer. The sealing is achieved through RF heating ofsusceptor composition 3302, which causes the inner layer 3212 to meltand bond to the container 3214. The advantage of replacing metallic foil3208 with susceptor composition 3302 is that now the container 3214 canbe inspected after it is sealed by using a metal detector or x-raymachine, and there are recycling advantages as well.

A conventional cap sealing construction is illustrated in FIG. 34. FIG.34 illustrates a polyethylene bottle 3402, a seal 3401, and a bottle cap3414. Seal 3401 includes several layers of substrate, including apolyethylene layer 3404, a metallic foil layer 3406, anotherpolyethylene layer 3408, a wax layer 3410, and a paper layer 3412. Seal3401 is adhered to bottle 3402 by heating foil through induction, whichcauses layer 3404 to weld to bottle 3402. As discussed above, it isdesirable to remove metallic foil layer 3406.

FIG. 35 illustrates an improved seal 3501 for bottle 3402. Seal 3501 isidentical to seal 3401 (see FIG. 34), except that the metallic foil 3406has been replaced with a composition 3502 according to the presentinvention. As discussed above, the advantage of removing metallic foil3406 is that now bottle 3402 can be inspected after it is sealed byusing a metal detector or x-ray machine, and can be more easilyrecycled;

Another use of the compositions described herein is to attach a flexiblebag 3602 containing dry food to an outer box 3604, as illustrated inFIG. 36. In one embodiment, flexible bag 3602 includes three layers,3610, 3611, and 3612, and outer box 3604 is a paper product, such as apaper board. To bond flexible bag 3602 to outer box 3604, an adhesivecomposition 3620 according to the present invention is placed betweenouter box 3604 and layer 3610. Adhesive composition 3620 is then exposedto an RF field that causes the composition 3620 to melt and flow andbond layer 3610 to outer box 3604. In one embodiment, layer 3610 is apolyethylene layer, layer 3611 is an EVOH barrier layer, and layer 3612is an EVA food contact layer. In another embodiment (see FIG. 37), outerbox 3604 is coated with a polyethylene layer (or other like layer) 3730.This configuration creates an improved bond.

C. Printing Applications

The susceptor compositions of the present invention may also be appliedtogether with one or more inks to provide writing, a design or graphic,e.g. as is described in U.S. Pat. No. Pat. No. 4,595,611. Particularapplication of this aspect of the invention is in the preparation ofink-printed substrates such as ovenable food containers. Examples ofpigments that can be combined with the susceptor composition includetitanium dioxide, iron oxide pigments, carbon black and organic pigmentssuch as isoindoline yellow. In a preferred embodiment, the susceptor isa sulfonated polyester. Alternatively, a sulfonated polyester-cationicdye salt may be employed as disclosed in U.S. Pat. No. 5,240,780. Thesubstrate may be printed once or multiple times to achieve the desiredresult. Once printed, the substrate may be further coated with a clearunpigmented composition which may comprise the susceptor composition ofthe invention. The same composition used to print may be used to furthercoat, but without the added pigments. The susceptor compositions may beRF activated after each printing/coating step, or after all of thecoatings are applied. Finally, the substrate may be coated with a clearpolyester sealing resin.

An extension the printing application is high speed inkjet used inprinters/copiers. Inks formulated as liquids (H-P/Cannon) or solid(Tetronic) composition can contain the susceptor compositions of thisinvention in amounts effective that can be activated by RF energy forrapid drying and fixing. Current ink formulations are too “slow indrying” or need excessive heat energy.

D. Bookbinding and Mailers

The susceptor compositions of the present invention may be used to bondpaper substrates used in printing and/or copying. An advantage of thepresent invention is that a substrate to be printed on (such as a papersubstrate) can be coated with a susceptor composition described hereinprior to printing on the substrate. For example, FIG. 43 illustrates aprocess for assembling a book, magazine, or periodical, or the like. Instep 4302, a portion of one side of a substrate is coated with asusceptor composition that functions as an adhesive. Any one of thevarious methods for coating a substrate described herein can be used tocoat the substrate. FIG. 44 illustrates a preferred portion of asubstrate to be coated with the susceptor composition. As shown in FIG.44, a thin strip of the susceptor composition 4404 coats one edge of thesubstrate 4402. The portion of the substrate that is not coated is theportion where ink will be printed. Preferably, the susceptor composition4404 is formulated such that it is tack free, however, this is not arequirement.

After the substrate 4402 has been coated, the substrate may be processedinto rolls, stacks and the like and stored for later use (step 4304). Instep 4306, the coated substrate is fed into a printing means that printsink onto the substrate. The printing means can be a conventional printeror conventional photocopying machine. Further, the substrate can be fedinto the printing means as a continuous substrate or as cut pieces. Forthis example, we will assume that cut pieces of the substrate are fedinto the printing means. In step 4308, after the printing means printsink onto a substrate, the substrate is stacked with the other substratesthat have already been fed into the printing means as shown in FIG. 45.The stack is placed in an electromagnetic field. The electromagneticfield causes the susceptor composition to melt and flow. The stack isthen nipped to assure a good bond (step 4312).

In one embodiment, prior to placing the stack in the electromagneticfield, the substrate stack is pressure bonded by applying upward and/ordownward pressure on the stack. In another embodiment, the ink that isprinted on the substrates includes a susceptor composition. In this way,the ink can be dried rapidly by passing the substrate through anelectromagnetic field;

In another embodiment, mailers or envelopes can be constructed.Referring to FIG. 46, a portion of one side of substrate 4602 is coatedwith a susceptor adhesive composition 4604. Preferably, the susceptoradhesive composition 4604 is formulated so that it is tack-free. Thesubstrate 4602 includes a fold line 4610. The coated substrate 4602 canbe fed into a printing means that prints ink onto the substrate. Afterthe ink is printed thereon, the substrate is folded along the fold line4610 so that the top portion 4612 of the substrate 4602 contacts thebottom portion 4614 of the substrate (see FIG. 47). At this point, thesubstrate is passed through the electromagnetic field so as to melt andflow the susceptor composition 4604, thereby bonding the top portion4612 of the substrate with the bottom portion 4614 when the susceptorcomposition 4604 solidifies.

E. Security Devices

As would be apparent to one skilled in the relevant art(s), the adhesiveof the present invention can be used to seal containers, casings,housings and the like (hereafter “container”). In particular, theadhesive of the present invention is preferably used to seal containersthat a manufacturer does not want accessed by others. A manufacturer maywant to prevent a third party from opening certain containers forsecurity, safety or quality control reasons. However, the inside of thecontainer must still be accessible to the manufacturer or qualifiedrepair facility. By exposing the seal to an electromagnetic field, themanufacturer can disassemble the container.

For example, a manufacturer may want to prevent an article intended forone-time use from being reused; As such, the adhesive of the presentinvention can be used, for example, to seal the shell or casing of adisposable camera. The manufacturers of such disposable cameras often donot want to have the shells reloaded and reused by the consumer or acompetitor company. If the adhesive of the present invention is used toseal the camera shell, then when the film developer opens the camerabody to remove and process the film, mating sections of the camera shellattached by the adhesive would break or deform such that the camera bodycould not be reused. As such, the adhesive of the present inventionwould prevent tampering with and unauthorized reloading of disposablecamera shells.

FIG. 48 shows an example of a container 4800 sealed with a susceptorcomposition of the present invention. Container 4800 includes a firstportion 4804 and a second portion 4808. In one embodiment, first portion4804 is a container base and second portion 4808 is a lid. Container4800 can be made from a variety of materials, including, for example,polypropylene, polystyrene, polyolefin, wood or wood products, rubber,plastics, glass, ceramics, paper, cardboard, natural or synthetictextile products, aluminum or other foils, metals, or any combination ofthese materials. An adhesive composition 4812, made in accordance withthe present invention, is applied to a surface of container 4800. In theexample of FIG. 48, adhesive composition 4812 is applied to a firstmating surface of first portion 4804. Second portion 4808 is then placedon top of first portion 4804, so that a second mating surface of secondportion 4808 comes in contact with adhesive composition 4812. A suitableelectromagnetic field, as described herein, is then applied to adhesivecomposition 4812 to join the first and second mating surfaces of firstand second portions 4804 and 4808.

To open container 4800, suitable RF energy must again be applied tocontainer 4800 to cause adhesive composition 4812 to reflow. If a personattempts to open container 4800 without applying the suitableelectromagnetic field, the container 4800 is designed to preferablybreak or catastrophically fail and so that it cannot be reused.

FIG. 49 shows another example of a device 4900 sealed or otherwisejoined together with a composition of the present invention. Device 4900includes a first portion or substrate 4904 and a second portion orsubstrate 4908. Device 4900 can be made of a variety of materials, asdiscussed above with respect to container 4800, shown in FIG. 48. Inthis embodiment, first substrate 4904 includes a male portion 4912forming the first mating surface. Male portion 4912 includes a narrowedsection 4916 and a wider section 4920. A corresponding female portion4924 forming a second mating surface is formed in second portion 4908and is configured to accommodate or receive wider section 4920 of maleportion 4912. Second portion 4908 may also be configured to accommodatea portion of narrowed section 4916.

An adhesive composition 4928, made in accordance with the presentinvention, is applied to the second mating surface of female portion4924 of second portion 4908. First portion 4904 is then assembled sothat the first mating surface comes in contact with adhesive composition4928 on second portion 4908 while the adhesive composition is within theelectromagnetic field. First portion 4904 is locked into second portion4908 once the application of electromagnetic filed is discontinued,causing adhesive composition 4928 to solidify. To disassemble device4900, an electromagnetic field must again be applied to adhesive 4928 tocause it to reflow and allow the portions 4904 and 4908 to separate. Ifsomeone attempts to disassemble device 4900 without application of asuitable electromagnetic field, narrowed section 4916 of male portion4912 will break or otherwise catastrophically fail resulting in device4900 being unusable. As such, this embodiment will prevent authorizeddisassembly and reuse of device 4900.

FIG. 50 shows another example of a device 5000 sealed or otherwisejoined together with a composition of the present invention. Device 5000is similar to device 4900 described above with respect to FIG. 49,except that an electronic circuit path 5004 is added to male portion4912 such that it is disposed through narrowed section 4916. As such,should portions 4904 and 4908 of device 5000 be disassembled withoutapplication of a suitable electromagnetic field, electronic circuit path5004 will be cut during failure of narrowed section 4916, resulting infurther failure of device 5000.

FIG. 51 shows still another example of a cross-section of a container5100 that has been sealed with the adhesive of the present invention.Container 5100 includes a first portion 5104 and a second portion 5108.Container 5100 can be made of a variety of materials, as discussed abovewith respect to container 4800, shown in FIG. 48. First portion 5104includes a protrusion 5112 which forms a first mating surface. In theembodiment shown in FIG. 51, protrusion 5112 extends around the entirecircumference of container 5100. However, it would be apparent to oneskilled in the relevant art that one or more discrete protrusions 5112could be used instead of or in addition to the continuous protrusion5112. Second portion 5108 includes a recess 5116which forms a secondmating surface corresponding to the first mating surface of protrusion5112. Protrusion 5112 and corresponding recess 5116 are formed slightlyinward of the periphery of container 5100 to so that when first andsecond portions 5104 and 5108 are joined, the mating surfaces and anadhesive composition 5120 therebetween cannot be accessed, therebyfurther reducing the risk of a person prying apart or otherwisedisassembling container 5100. Adhesive composition 5120, made inaccordance with the present invention, is applied to the second matingsurface of recess 5116. First and second portions 5104 and 5108 can bejoined together by application of suitable electromagnetic field andsimilarly disassembled by re-application of the electromagnetic field.

The invention relates to an apparatus, comprising:

a first portion having a first mating surface;

a second portion, having a second mating surface;

a composition disposed between the first mating surface and the secondmating surface, wherein the composition comprises a susceptor and apolar carrier wherein the susceptor and/or the polar carrier are presentin amounts effective to allow the composition to be heated by RF energy,and wherein the composition adheres the first mating surface to thesecond mating surface such that application of a force to separate thefirst mating surface and the second mating surface results in breakageof the apparatus unless the composition is in a melted state.

In this apparatus, the composition may be disposed on the first matingsurface and the second mating surface such that the composition is notaccessible when the first and second mating surfaces are joined. Inanother embodiment, the first mating surface may comprise a protrusiondisposed on the first portion. In another embodiment, the second matingsurface may comprise a recess formed in the second portion. In a furtherembodiment, the apparatus may further comprise an electronic circuitpath disposed in the protrusion. In another embodiment, the firstportion and the second portion are disassembled upon application of anelectromagnetic energy to the composition.

F. Thermal Destruction

The susceptor composition of the present invention can not only be usedto coat a substrate and bond adherands, but also can be used to cut asubstrate. A substrate can be cut using a susceptor compositiondescribed above by first applying the susceptor composition to at leastone side of the substrate. Next, an electromagnetic field is applied tothe susceptor composition causing the susceptor composition to heat. Thethermal energy generated by the susceptor composition heats thesubstrate,.particularly the section of the substrate that is in contactwith the susceptor composition. The substrate is heated until a sectionof the substrate melts resulting in the substrate being cut.

In this embodiment, the invention relates to a method for cutting asubstrate, comprising:

applying a composition to a portion of the substrate, wherein thecomposition comprises a susceptor and polar carrier wherein thesusceptor and/or the polar carrier are present in amounts effective toallow the composition to be heated by RF energy, and wherein the portionof the substrate defines a first section of the substrate and a secondsection of the substrate;

melting the portion of the substrate, wherein the melting step includesthe step of heating the composition, wherein the step of heating thecomposition includes the step of applying RF energy to the composition;

after the portion of the substrate has begun to melt, applying a forceto the substrate to separate the first section from the second section.

G. Seam Sealing

The susceptor compositions of the present invention may be used to sealthe seams of products made from cloth. Conventional cloth materialsmanufactured from man made or natural fibers are sewn together to formcloth products, such as clothing, bags, tents, awnings, covers, and thelike. Typically, the seams of cloth products such as tents, awnings,bags, etc. need to be sealed to prevent leakage of liquids through thesmall holes in the products created by a sewing needle and thread duringa stitching process. The susceptor compositions of the present inventioncan be used to seal these seams.

FIG. 62 illustrates how a susceptor composition of the present inventioncan be used to seal the seams of cloth products. FIG. 62 illustrates aseam sealing system 6200 for sewing a first cloth material 6202 to asecond cloth material 6204 and for sealing the seam. In one embodiment,a susceptor composition 6206 according to the present invention isplaced between the first and second cloth materials 6202 and 6204. Inanother embodiment, either one or both of the cloth materials 6202 and6206 are coated with the composition in the location where the seam willexist.

The system includes a pressure plate 6208 and a reciprocating needle6212, through which a thread 6210 can be threaded, for joining the firstcloth material 6202 with the second cloth material 6204. The seamsealing system 6200 also includes an RF heating system according to thepresent invention for activating the composition 6206. The RF heatingsystem includes a reciprocating pressure foot 6214 and at least twoprobes (not shown) placed within and near the surface of the pressureplate 6208. The probes (not shown) are connected to the power supply 502for generating an RF field at the probes. Alternatively, the probes canbe located within the pressure foot 6214 as opposed to the pressureplate 6208.

The cloth materials 6202 and 6204 and the composition 6206 are pulledpast the reciprocating needle 6212 and then past the reciprocatingpressure foot 6214. The reciprocating needle 6212 and thread 6210 stitchthe first material 6202 to the second material 6204, thereby joining thematerials together at a seam. This stitching process creates small holesin the materials 6202 and 6204. The RF field generated at the probeswithin the pressure plate 6208 activates the composition 6206, whichcauses the composition 6206 to flow and thereby fill or cover the smallholes created by the needle 6212 during the stitching process. Thereciprocating pressure foot 6214 functions to evenly flow the activatedcomposition 6206, thereby facilitating the composition in thefilling/covering of the holes created by the needle 6212. In thismanner, the susceptor compositions of the present invention can be usedto seal seams.

XII. Kits

The invention also provides kits for use in the preparation of thebonding composition according to the present invention. Kits accordingto the present invention comprise one or more containers, wherein afirst container contains a susceptor composition of the invention.Additional kits of the invention comprise one or more containers whereina first container contains a susceptor as described above and a secondcontainer contains one or more adhesive compounds and/or carriers, suchas water, glycerine, N-methyl pyrrolidone (NMP), dimethylformamide(DMF), dimethylacetacetamide (DMAC), dimethylsulfoxide (DMSO),tetrahydrofuran (THF), polyvinyl pyrrolidone (PVP),polyvinylpyrrolidone/vinyl acetate copolymer (PVP/VA), and branchedpolyesters. The kits of the invention may be used to produce one or moreof the bonding compositions of the present invention for use in avariety of applications as described below.

The invention also provides for kits comprising at least two containers,wherein one of the containers comprises a susceptor and another of thecontainers comprises a polar carrier, wherein when the susceptor and thecarrier are applied to substrates and the applied susceptor and carrierare interfaced, a composition is formed that is heatable by RF energy.

XIII. Experimental Set-up

FIG. 40 shows an example experimental set-up utilized to test thesusceptor compositions described above with respect to example 4. An RFsignal is generated by a signal generator 4001. Signal generator 4001can be an HP 8165A signal generator (available from Hewlett PackardCorporation). The RF signal is coupled to the input side of RF poweramplifier 4002 (available from ENI). The RF power is fed from the outputside of RF power amplifier 4002 to the input side of an impedancematching circuit 4063 that functions to match the output impedance tothe combined load impedance of coil 4004 and test sample 4005. Impedancematching circuit 4003 can be designed according to known electronicsprinciples as would be apparent to those of skill in the art. See, e.g.,“The Art of Electronics,” by P. Horowitz and W. Hill, Second Ed.,Cambridge University Press (1994), especially Chapter 40, incorporatedby reference herein. The RF power of load coil 4004 was inductivelycoupled to test sample 4005. The frequency of signal generator 4001 wastuned to result in resonance at load coil 4004. This frequency wasdetected by a single turn, 2 inch diameter probe loop 4007, which waslocated just below and in proximity to load coil 4004. Resonance wasindicated by a maximum resulting voltage drop across probe loop 4007,and was displayed on an oscilloscope 4006, such as a model numberOS7020A. oscilloscope available from Goldstar. Frequency tuning wasperformed at sufficiently low RF powers in order to avoid heating oftest sample 4005. Once the frequency of signal generator 4001 was tunedto resonance, the RF power delivered to load coil 4004 was increased toa desired power level by increasing the output level of signal generator4001. The front panel of RF power amplifier 4002 displayed the measuredRF power level delivered to test sample 4005.

FIG. 41 illustrates another experimental heating system 4100. Heatingsystem 4100 includes a signal generator 4102. Signal generator 4102 canbe an HP 8165A signal generator (available from Hewlett PackardCorporation). Signal generator 4102 is used to generate a low levelradio frequency signal having a frequency between 10 MHz and 15 MHz.Signal generator has a control panel 4103 that allows a user to manuallyselect the frequency of the generated radio frequency signal. The outputlevel of the signal is also controllable from control panel 4103, orfrom a controller 4114. The output level of the generated RF signal canvary from 0 Volts to 1 Volt peak to peak into 50 ohms, or 0 dBm.

Controller 4114 is interfaced to signal generator through a generalpurpose interface board (GPIB) (not shown). In one embodiment,controller 4114 is a personal computer (PC) running the Windows®operating system. A visual C++ program that provides a user interfacefor controlling the output level of signal generator 4102 is configuredto run on controller 4114.

The low level RF signal generated by signal generator 4102 is providedto the input of a broadband RF amplifier 4106 using a coaxial cable4104. Preferably, broadband RF amplifier 4106 is the A1000 broadbandamplifier sold by ENI of Rochester, N.Y., and coaxial cable 4104 is astandard RG58 coaxial cable. Broadband Amplifier 4106 amplifies the lowlevel RF signal by 60 dB, thereby providing a 1 Kilowatt output into a50 ohm load for a 1 milliwatt (0 dBm) input. If the low level RF inputsignal provided to amplifier 4106 consists of a timed pulse, amplifier4106 will amplify the pulse to produce a high level pulse output.

Connected to the output of broadband amplifier 4106 is a directionalcoupler 4110. A suitable directional coupler can be purchased fromConnecticut Microwave Corporation of Cheshire, Conn. Directional coupler4110 is connected to the output of amplifier 4106 through an RF cable4107, such as an RG393 RF cable. The output of directional coupler 4110is connected to an impedance matching circuit 4122 using RG393 RF cable4112.

The function of impedance matching circuit 4122 is to match a 50 ohminput impedance to a variable impedance of probes 602 and 604 and thesample 410. Typical impedances of probes 602 and 604 in combination withsample 410 range from 200 ohms up to, 500 ohms.

Directional coupler 4110 has a reflected power output port 4111 that isconnected to an oscilloscope 4118. Preferably, oscilloscope 4118 is aTDS210 digital real time oscilloscope available from Tektronix, Inc.Directional coupler 4110 provides a signal representing the amount ofreflected power to oscilloscope 4118, which then displays the magnitudeof the reflected power.

The process for heating sample 410 using heating system 4100 will now bedescribed. Initially, an operator interacts with a user interface oncontroller 4114 to activate signal generator 4102 so that it produces a50 millivolt RF signal. The reflected power is then observed onoscilloscope 4118. The frequency of the 50 millivolt RF signal andmatching circuit 4122 are adjusted such that the reflected power isminimized. Once the frequency and the matching circuit are adjusted suchthat the reflected power is minimized, the signal generator is turned off and sample 410 is placed close to probes 602 and 604.

Next, controller 4114 is used to turn on signal generator 4102 so thatit once again produces a 50 millivolt RF signal. At this point, thefrequency and matching circuit are adjusted again until the reflectedpower is minimized. On achieving the minimum reflected power, signalgenerator 4102 is turned off. Next, operator uses controller to directsignal generator to produce an RF signal with a voltage ranging from 100millivolts to 1000 millivolts and with a pulse time of between 20milliseconds and 1000 milliseconds. This low level RF signal isamplified by broadband amplifier 4106. The amplified signal is thenprovided to impedance matching circuit 4122 and an a RF pulsedelectromagnetic field is produced at probes 602 and 604. The presence ofthe pulsed electromagnetic field causes sample 410 to heat.

FIG. 42 illustrates probes 4202 and 4204, which were the probes utilizedto test the compositions described herein. The present invention is notlimited to this or any particular probe design. Probe 4202 and probe4204 are both ⅛ inch square copper tubes. Probe 4202 and probe 4204 bothrest on a block 4250 of non-electrically conductive material,preferably, but not limited to, TEFLON™. More specifically, block 4250has ⅛ inch square; slots milled therein so that probes 4202 and 4204 arerecessed into block 4250.

Probe 4202 has a proximal section 4209, a center section 4210, atransition section 4211, and a distal section 4212. Similarly probe 4204has a proximal section 4213, a center section 4214, a transition section4215, and a distal section 4216. Center section 4210 is parallel withcenter section 4212. The center to center distance between centersection 4210 and center section 4212 is on half of an inch.

Proximal section 4209 diverges away from probe 4204. Similarly, proximalsection. 4213 diverges away from probe 4202. The center to centerdistance between the proximal end of proximal section 4209 and theproximal end of proximal section 4213 is about at least one and threesixteenths of an inch.

Distal section 4212 is parallel with distal section 4216 and parallelwith center section 4210. The center to center distance between distalsection 4212 and distal section 4216 is about at least one and threesixteenths of an inch. Transition section 4211 is between center section4210 and distal section 4212. Similarly, transition section 4215 isbetween center section 4214 and distal section 4216.

The reason the distance between the proximal end of proximal section4209 and the proximal end of proximal section 4213 is about at least oneand three sixteenth of an inch is to prevent arcing at the ends of probe4202 and 4204. For that same reason the distance between distal section4212 and distal section 4216 is about at least one and three sixteenthof an inch.

XIV. Examples

Without further elaboration, it is believed that one skilled in the artcan using the preceding description, utilize the-present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative and not limitative ofthe remainder of the disclosure in any way.

EXAMPLE 1

Various susceptor compositions were screened for use at frequencies fromabout 4 MHz to 15 MHz, and at power levels from about 0.5 kW to 1 kW. RFfrequencies of less than about 15 MHz are much less costly to produceand operate than RF frequencies of greater than 15 MHz. The best resultsconsistently occurred at the upper ends of the experimental frequencyand power ranges (e.g., 15 MHz and 1 kW). See FIG. 6 for a schematicdiagram of the experimental set-up and equipment used for the varioustests described herein. According to the present invention, a preferredcomposition comprises a uniform solution of PVP, NMP, and SnCl₂. Asuitable susceptor composition comprises SnCl₂ present in aconcentration of from about 1% to about 50%, NMP in a concentration offrom about 25% to about 75%, and PVP in a concentration of from about 1%to about 35%. These three components are soluble in one another. Thesecomponents were mixed together to form a uniform solution that was ableto be heated from about 75° F. to a boiling point of about 280° F. inseveral seconds. Acceptable results can also be obtained, for example,by substituting similar concentrations of PVP/vinyl acetate copolymerfor PVP, and substituting similar concentrations of lithium perchloratefor SnCl₂. In addition, other suitable compositions include a mixturecomprising ethylene/vinyl acetate copolymer in a concentration of fromabout 75% to about 99% and ethylene/acrylic acid copolymer in aconcentration of from about 1% to about 25%, a mixture comprisingLiC₂H₃O₂ in a concentration of from about 1% to about 25%,ethylene/vinyl acetate copolymer in a concentration of from about 50% toabout 98%, and styrenated ethylene/acrylic acid copolymer in aconcentration of from about 2% to about 25%, and a mixture comprisingPVP/vinyl acetate copolymer in a concentration of from about 5% to about35%, SnCl₂ in a concentration of from about 5% to about 49%, and NMP ina concentration of from about 1% to about 90%. Other compositionconstituent concentrations will be apparent to those of skill in the artbased on the present description.

In this example, a preferred susceptor composition comprising. SnCl₂ ina concentration of about 33%, NMP in a concentration of about 50%, andPVP in a concentration of about 17% was prepared to bond variouscombinations of thin polyolefin layers of polypropylene (PP) andpolyethylene (PE). This example susceptor composition resulted in auniform dispersion of salt ions in a polymeric adhesive.

The experiment was conducted by saturating a second carrier, a thinlayer of an insoluble porous carrier (in this example non-woven PP),with a small amount of the susceptor composition. The example salt-basedsusceptor composition provides a continuous matrix of salt ions in apolar organic medium throughout the insoluble porous carrier. As shownschematically in FIG. 3, the insoluble porous carrier 302 was sandwichedin-between two layers of PP or PE, layers 304 and 306, respectively, andthen transversely heated by the application of RF energy. By RF heatingat about 14-15 MHz for about 1-2 seconds at about 0.8-1 kW of poweroutput, sufficient bonding occurred between the non-woven PP carrier andthe layers of PP and PE. In this example, the strength of the bondedregion was at least as strong or stronger than the PP or PE substratesthemselves. The polyolefin layers to be bonded were chosen fromcombinations of (1) PP non-woven and (2) PE film. The results of thisexample are shown below in Table 1.

TABLE 1 insoluble porous carrier (saturated with PVP, NMP and SnCl₂)bonding results PP non-woven/PP non-woven bonding within 1-2 seconds PEfilm/PE film bonding within 1-2 seconds PP non-woven/PE film bondingwithin 1-2 seconds

For each combination, the saturated insoluble porous carrier bonded theouter layers in about 1-2 seconds. There was evidence of melting in theouter layers, with some minor substrate distortion and tiny melt holes.By using the saturated PP non-woven carrier, a uniform matrix of theadhesive and susceptor components resulted in intimate contact betweenthe adhesive component and both outer layers.

EXAMPLE 2

The susceptor composition utilized in this example comprised SnCl₂ in aconcentration of about 33%, dissolved in a mixture of NMP in aconcentration of about 50% and PVP in a concentration of about 17%.Various PP and PE substrate surfaces were coated with the RF susceptorcomposition, including: (1) PP non-woven and (2) PE film. The susceptorcomposition was hand drawn onto each surface as a wet layer that wouldeventually dry, leaving a coating which was dry to the touch. RF heatingtests were performed on the coated substrates. In each case, two likesamples were placed together with the coated surfaces in contact withone another. The contacted surfaces were placed in a load coil that wasdesigned to clamp the surfaces firmly together and transversely heat a0.25 inch×8 inch strip of the susceptor composition. The operatingfrequency was about 14 MHz, and the power delivered to the coil wasabout 1 kW. The tests were split into two parts: using a wet susceptorcomposition and using a vacuum dried susceptor composition. The resultsare shown in Table 2.

Vacuum drying was employed in this experiment as an extreme experimentalcondition for comparison purposes, but is not expected to represent acommercial embodiment.

TABLE 2 Coated Substrates in Contact, Under 1.2 kW RF at 14 MHz WET/DRYnon-woven PP/ PE film/ Substrates non-woven PP PE film WET successfullyevidence of bonded together melting, slight within 1-2 seconds bondingat edges of the coat of susceptor material VACUUM No evidence of Noevidence of DRIED heating after 1 heating after 1 minute. minute.

The results show that the wet susceptor composition generates enoughheat within 1-2 seconds at 14 MHz and 1 kW to melt the PP non-woven orPE film in transverse heating of thin hand drawn films. Bonding issuccessful between layers of PP non-woven. As layers of PP non-woven arebrought together, the susceptor composition is displaced into the openspace between the fiber of the PP non-woven layers, allowing the twolayers of PP non-woven to come together and make intimate contact,enabling bonding during re-flow of the layers.

Complete bonding was not demonstrated between layers of PE film. Aslayers of PE film were brought together, the susceptor mixture behavedas a hydrostatic middle layer or boundary, preventing intimate contactbetween the two outer polyolefin layers. It was observed that thematerial in the layers of PE was more likely to partition away from thesusceptor composition than to cross the susceptor composition layerduring melting and re-flow. It was also observed that as the susceptorcomposition was vacuum dried, it lost its ability to be RF heatedeffectively. Results were likely due to one or more of the followingfactors: the precipitation of ions back into an inactive salt as thesolvent volatilizes to form the dry coat; a decrease in translationalmobility of any ions still supported by the dry coating, thus preventingRF heating from occurring; and, in the case of PE films, an insufficientintermolecular contact due to the smoothness of the films. According tothe present invention, this problem can be solved by introducing anadditive, such as a surfactant, nonvolatile solvent or, plasticizer tothe composition, to achieve better attachment.

EXAMPLE 3

In this example, an RF activated susceptor composition was prepared froman EASTMAN AQ branched polyester (available from the Eastman ChemicalCorporation) and an aqueous solution of SnCl₂. Various layers of PPnon-woven and PE film were tested. The susceptor composition that wasused in this example comprised SnCl₂ dissolved in distilled water. Thissolution was blended with a branched polyester adhesive component,EASTMAN AQ35S. Suitable concentrations of the branched polyester rangedfrom about 25% to about 75%.

In a series of experiments, the susceptor composition was used to adhereall combinations of (1) PP non-woven and (2) PE film substrates. In eachexperimental combination, the composition was first coated onto the twosubstrate surfaces and dried under ambient conditions similar to thoseused in commercial practice. The two substrates were then pressedtogether in the work coil with the two susceptor composition coatedsurfaces in contact with each other. The coated surfaces were not tackyenough at this point to result in contact adhesion between thesubstrates. All combinations of substrates were successfully adhered toone another by RF heating for a period of about 1 second at about 14 MHzand about 1 kW. The substrates were adhered to each other by theRF-activated susceptor composition, instead of being bonded by re-flowof the substrate. No apparent melting or distortion of the substrateoccurred. This example demonstrates that a susceptor composition coatingcan be dry to the touch and still be activated by RF heating.

EXAMPLE 3a

Analogous to Example 3 above, the active ingredients Eastman AQ35S andSnCl₂ (in constituent concentrations consistent with the parametersdescribed above) were dissolved in NMP to form a susceptor composition.The composition was coated on a PP non-woven web and was allowed to airdry. The slightly tacky web was placed between polyolefin substrates andthe assemblies were RF heated in the RF work station at 14.65 MHz andabout 0.8 kW for 5 seconds. Good adhesion was obtained in each case.

EXAMPLE 3b

A susceptor composition capable of inductive activation was preparedwith an aqueous dispersion of a sulfopolyester, EASTEK 1300 Polymer(available from Eastman Chemical Company), by addition of SnCl₂. Aprecipitate was recovered from this mixture and a film from thisprecipitate was obtained by pressing between hot platens at about 200°F. and 1000 psi for a short time. This film was slightly wet and wassandwiched between a PE film and a PP non-woven web. The assembly was RFheated in the RF work station at 14.63 MHz and about 0.8 kW for 1second. Good adhesion without substrate deformation was achieved.

EXAMPLE 3c

Analogous to Example 3b, additional experiments were performed in whichslightly wet-to-touch thin films of the susceptor compositions ofexample 3b were sandwiched between two stacks consisting of multiplelayers of non-woven PP or multiple layers of non-woven PP laminated toPE film. Three different types of sandwiched assemblies were tested,including: (1) 8 layers of non-woven PP/susceptor composition/8 layersof non-woven PP, (2) 2 layers of PP non-woven laminated to PEfilm/susceptor composition/2 layers of PP non-woven laminated to PE film(with PP non-woven facing PE film at the stack interface), and (3) 4layers of PP non-woven/susceptor composition/4 layers of PP non-woven.In each case, the assemblies were RF heated in the RF work station at14.63 MHz and about 0.8 kW for 1 second. In all cases, good adhesionoccurred between the multilayer stacks without causing distortion to thestacks.

In this experiment, each multilayered stack was pre-assembled using aconventional contact adhesive, and the two stacks were later adhered toone another using the susceptor composition. However, it is contemplatedin the practice of the invention that each multilayer stack can bepreassembled using a susceptor composition to either simultaneously orsequentially bond or adhere the various layers of each stack.

EXAMPLE 4

Based on the success of the susceptor compositions tested in Examples1-3b, other susceptor compositions were made and tested. In thisexample, sample compositions (in constituent concentrations consistentwith the parameters described above) were tested in half-filled testtubes nearly centered within the coil of the RF equipment described inFIG. 40. Various settings for voltage input and frequency of the currentwere investigated. Table 3 summarizes the results of these experiments.The effectiveness of RF heating is shown by the time required for thesamples to boil or to rise to the indicated temperature.

TABLE 3 Selected Test Tube Experiments with Potential SusceptorsFrequency, Input, Field, Time to boil or Materials MHz mV V temperaturerise Solid Salts SnCl₂ × 2H₂O 13.73 300 7.8 Poor heating SnCl₂ × 2H₂O13.73 600 15 39 sec., 122° F. SnCl₂ 13.74 800 ˜20 Poor heating LiClO₄ ×3H₂O 13.74 800 ˜20 10 sec. Aqueous Solutions Distilled Water 13.75 80080 sec., 117° F. LiClO₄ 13.73 800 ˜20  3 sec. SnCl₂ 800 ˜20  5 sec. NaCl13.67 800 ˜2.2  3 sec. NaCl 5.833 320 ˜2.2 20 sec. NaCl 3.719 10 58 30sec. Li-acetate 13.73 1000 10 sec. Nonaqueous Solutions NMP 13.74 800 60sec., 89° F.  NMP/SnCl₂ 13.74 800 47 sec., 350° F. NMP/PVP/SnCl₂ 13.73685 20  8 sec., 142° F. NMP/PVP/LiClO₄ × 13.73 643 20  6 sec., 135° F.3H₂O NMP/PVP/Li-acetate × 13.73 600 18 18 sec. 2H₂O Liquid SamplesUni-REZ 2115 13.75 1000 75 sec., 126° F. MICHEM 4983 13.77 10 40 30sec., 178° F. MICHEM ACRYLIC 1 13.73 800  4 sec.

These tests show that, as expected, aqueous solutions of varioussusceptors, such as salts, coupled very well with the RF energy. Alltested susceptor compositions came to a boil within 3-30 seconds. Asdiscussed above, SnCl₂ dissolved in NMP also coupled very effectively.Although a boiling time of 47 seconds is shown in this experiment, thetemperature of 350° F. reached by this mixture is substantially higherthan is required for heat bonding polyolefins.

In the section on nonaqueous solutions in Table 3, it can be seen thatwhile NMP is only a weak susceptor in its own right, it couples veryeffectively with the RF energy, when a variety of salts are dissolved init. It was also observed that the solution's ability to solubilize saltsseems to be enhanced when PVP is dissolved in it. Since the compositionsshown in Table 3 were not optimized, the RF heating capability of thesolutions appear to be very good.

The last section of Table 3 shows the RF heating capability of someliquid polymers. They range from very mild coupling ability to verypowerful coupling ability in the case of MICHEM ACRYLIC 1 (availablefrom Michelman Corporation), a styrenated ethylene-acrylic acid polymer.

EXAMPLE 5

This experiment tested the compatibility of various film forming andadhesive polymers with modifying resins and additives and with inorganicor organic susceptors (in constituent concentrations consistent with theparameters described above). A series of -experiments were conductedwith low-density polyethylene (LDPE) as the substrate, as summarized inTable 4.

TABLE 4 Bonding Feasibility Experiments With a Low Density PolyethyleneSubstrate Frequency, Input, Sample MHz mV Time Adhesion Substrate ELVAX40W + 14.55 500  1 min.  None LDPE UNI-REZ 2641 ELVAX 40W + TheLi-acetate did not mix with the polymers under UNI-REZ pressingconditions 2641 + Li-acetate ELVAX 40W + 14.54 500  1 min.  None LDPEN,N-ethylenebis- stearamide @ 80/20 ELVAX 40W + 14.54 650  1 min. Slight LDPE N,N-EbSA @ 80/20 + MICHEM ACRYLIC 1 MICHEM 14.54 650 30 sec.Slight LDPE ACRYLIC 1 PRIMACOR The Li-acetate did not mix with thepolymers under 3460 + Li-acetate pressing conditions N,N-EbSA + 14.6 85030 sec. Partial LDPE ELVAX 40W + Poly (ethylene- maleic anhydride) + Li-acetate + MICHEM PRIME 4983 ELVAX 40W + 14.6 850 30 sec. Partial LDPELi-acetate + MICHEM PRIME 4983 ELVAX 40W + 14.6 850 15 sec. Partial,LDPE MICHEM good PRIME 4983 UNI-REZ 2641 14.6 850 30 sec. Partial, LDPEgood ELVAX 40W + 14.6 850 30 sec. Partial, LDPE UNI-REZ 2641 + goodMICHEM PRIME 4983 Polyethylene 14.6 850 15 sec. Partial, LDPE (AS) +good AlliedSignal GRADE A-C + MICHEM PRIME 4983 Polyethylene 14.6 850 30sec. Partial, LDPE (AS) + MICHEM good PRIME 4990 ELVAX 40W + 14.6 850 30sec. None LDPE Fe₂O₃ ELVAX 40W + 14.6 850 15 sec. Good LDPE MICHEM PRIME4990 ELVAX 410 + 14.6 850 30 sec. None LDPE N,N-EbSA + PEMA ELVAX 410 +14.6 850 30 sec. None LDPE N,N-EbSA + PEMA + KEN-REACT LICA 44 ELVAX410 + 14.6 850 10 sec. Partial, LDPE N,N-EbSA + good PEMA + MICHEMACRYLIC 1 ELVAX 40W + 14.6 850 15 sec. Good LDPE Li-acetate/ MICHEMACRYLIC 1 (paste) ELVAX 40W + 14.6 850 15 sec. Good LDPE MICHEM ACRYLIC1 ELVALOY EP 14.6 850 30 sec. None LDPE 4043 MICHEM ACRYLIC 1 ELVAX40W + 14.6 850 30 sec. None LDPE UNI-REZ 2641 + STEROTEX HM wax + MICHEMACRYLIC 1 SnCl₂ + NMP + 14.54 850 10 sec. None Mylar/dry PVP K29-30 +0.1% 14.54 850 30 sec. None Mylar/dry SURFYNOL 104PA

Several susceptors which had been very effective in test tube runs didnot always lead to good bonding or adhesion in these trials. MICHEMACRYLIC 1 is a good example. Likely reasons include: (a) the susceptorswere only effective wet and lost their coupling ability when used in adry film, or (b) the susceptor itself was not a good adhesive and formeda barrier to melted PE bonding to itself. There was an indication thatthe second reason prevailed when it was shown that the susceptorsperformed better when blended with PE or EVA which could act as hot meltadhesives for the substrates. Better results were obtained with MICHEMPRIME 4983 and 4990, MICHEM ACRYLIC 1, and UNI-REZ 2641 in combinationwith either PE or EVA. However, N,N-ethylene-bisstearamide, which wasdescribed in the Degrand reference, was not very effective in theseexperiments. A number of trials provided partial adhesion, as noted inTable 4, which were likely caused by the inability of the film holder toclamp the substrates tightly and flat. Although the shortest successfulheating times were on the order of 10 to 15 seconds, which would be toolong for a commercial operation, the results are positive, in that boththe adhesive compositions and the operation of the film station can befurther optimized without undue experimentation.

EXAMPLE 6

Another series of experiments were performed with other polyolefinsubstrates, including a PP nonwoven. These trials are summarized belowin Table 5. Very good bonds were obtained with several compositions atdwell times down to about 1 second. While this may be too long for somecommercial applications, it is highly encouraging for trials that werenot optimized with regard to either the susceptor composition or thetest equipment.

TABLE 5 Bonding Experiments With Polyolefin Substrates Frequency, Input,Sample MHz mV Time Adhesion Substrate ELVAX 40W 14.61 850 30 sec. NonePP (Du Pont 40% nonwoven vinyl acetate to polyethylene) ELVAX 40W +14.61 850 15 sec. Good PP MICHEM nonwoven PRIME 4990 ELVAX 40W + 14.61850 30 sec. None PP UNI-REZ 2641 + nonwoven STEROTEX HM wax + MICHEMACRYLIC 1 ELVAX 40W + 14.61 850 15 sec. Good PP UNI-REZ 2641 + nonwovenMICHEM ACRYLIC 1 SnCl₂ + NMP + 14.61 850  1 sec. Good PP PVP nonwovenK29-30 + 0.1% SURFYNOL 104PA (Dried 90 min) 14.61 850  5 sec. Good PPnonwoven (Dried 15 hrs) 14.61 850 25 sec. None PP nonwoven (Dried 15hrs + 14.61 850  2 sec. Good PP NMP) nonwoven SnCl₂ + NMP + 14.61 850  1sec. None PE/PE PVP K29-30 + 0.1% SURFYNOL 104PA SnCl₂ + NMP + 14.61 850 1 sec. Slight PP/PP n/w PVP 14.61 850  2 sec. Good PP/PP n/w K29-30 +0.1% SURFYNOL 104PA ELVAX 40W + 14.61 850 30 sec. None PP UNI-REZ 2641 +nonwoven Indium tin oxide SURFADONE 14.61 850 30 sec. None PP LP-300 +SnCl₂ nonwoven PVP/VA S-630 + 14.61 850  1 sec. Good PP SnCl₂ + NMPnonwoven 14.61 850  1 sec. Slight PE/PE PVP/VA S-630 + 14.61 850  1 sec.Good PP SnCl₂ + NMP + nonwoven Fumed silica 14.61 850  5 sec. SlightPE/PE 14.61 850  2 sec. Slight PP/PP n/w ELVAX 40W + 14.61 850 30 sec.None PP UNI-REZ 2641 + nonwoven Li-acetate, pressed Li-acetate × 14.61850 30 sec. None No 2H₂O melting Mg(NO₃)₂ × 14.61 850 30 sec. None No6H₂O melting MgAc × 4H₂O 14.61 850 30 sec. None No melting Stearicacid + 14.61 850  2 sec. None PP Cetyl alcohol + nonwoven Mg(NO₃)₂ ×14.61 850 10 sec. Good PP 6H₂O nonwoven EVA AC-400 + 14.61 850 2,5 andNone PP SURFADONE 10 sec. nonwoven LP-300 + SnCl₂

Some of the better results were obtained with compositions containingPVP or PVP/VA and SnCl₂ salt dissolved in NMP (in constituentconcentrations consistent with those discussed above). It was shown,however, that thorough drying of the susceptor composition eliminatedits ability to couple with the RF field. It appears that the mobility,provided by the presence of at least a small amount of NMP solvent, isimportant for efficient coupling to the applied RF field. This mobilityfunction can be provided by the selection of an appropriate nonvolatileplasticizer, such as epoxidized oils, polyhydric alcohols, substitutedamides, sulfonamides, aryl and alkyl aryl phosphates, polyesters and awide variety of esters, including benzoates, phthalates, adipates,azelates, citrates, 2-ethylbutyrates and hexoates, glycerides,glycollates, myristates, palmitates, succinates, stearates, etc.Plasticizers are used to solvate a material, and thus improve itsmolecular mobility if it has become too rigid.

In general, ethylene co-polymers with functionality providing (a)enhanced compatibility and (b) ionic or highly polar constituents areeffective in bonding or adhering substrates, together with salts thatare either soluble or readily dispersed in the polymer matrix. There isalso evidence that in some compositions mobility of the dipoles must beassured. This was achieved in the presence of such high-boiling solventsas NMP. It can also be extrapolated that other high boiling solvents ornon-volatile plasticizers can achieve the same effects with morereproducible results.

These example susceptor compositions utilize a combination of polarcomponents and hydrated salts in a polymer matrix plasticized with highboiling and high dielectric constant additives that are activatable at arelatively low frequency of about 15 MHz.

The methods and experiments set forth above will allow those of skill inthe art to determine without undue experimentation that a particularmixture would be suitable for bonding or adhering substrates accordingto the present invention.

EXAMPLE 7

This example demonstrates RF-heatable thermoplastic compositions derivedfrom the combination of various ion-containing polymers with glycerin.These compositions are shown to be significantly more susceptible to RFheating than either the component ion-containing polymers or glycerinare by themselves.

EXAMPLE 7a

Several compositions comprising 70 wt % sulfonated polyesters in 30 wt %glycerin were prepared. Each sample was prepared by first mixing 14grams of sulfopolyester material with 6 grams of glycerin in a 60milliliter glass jar. The open topped jar was heated in a convectionoven at 165 C. for 1 hour. After thirty minutes, the composition wasremoved from the oven and hand stirred for 1 minute and then immediatelyreturned to the oven. After an additional 30 minutes of heating at 165C., the composition was removed from the oven and hand stirred for 1minute. While the composition was still molten, it was hand-drawn into a1 inch wide by 3 inch long by 0.006 inch thick coating on the surface ofa 0.004 inch thick sheet of transparency film (PP2500 series 3Mtransparency film) that was supported on a 180° F. 10 inch×10 inchCorning model PC620 hot plate. Immediately after the composition wascoated to the film, the coated film was removed from the hot plate andallowed to cool to room temperature. The samples were then evaluated forfilm properties and RF heating.

The RF equipment setup used for testing this example and examples 8-16consisted of the RF probes described in FIG. 42 and the RF equipmentdescribed in FIG. 41. Unless otherwise noted, in each case a1-inch×3-inch sample (410) was placed over the RF probes as shown inFIG. 41. The distance from the surface of the probes to the sample wasabout 0.016 inches. The sample was heated at about 1 KW input power intothe tuned heat station 4122 (or impedance matching circuit 4122) atabout 13.5 MHz for the time required to cause observable heating andmelting in the activation region of the RF probes.

TABLE 6 Film Time to Melt Experiment # Composition DescriptionProperties (s) BRANCHED SULFONATED POLYESTERS . . . (Eastman APolyesters, Available from Eastman Chemical Company, Kingsport, TN, USA)1 70 wt % AQ1045 Clear, tacky, 0.25 30 wt % glycerin flexible. 2 70 wt %AQ1350 Clear, tacky, 0.25 30 wt % glycerin flexible. 3 70 wt % AQ1950Clear, tacky, 0.25 30 wt % glycerin flexible. 4 70 wt % AQ14000 Clear,tack, 0.25 30 wt % glycerin flexible. LINEAR SULFONATED POLYESTERS . . .(Eastman A Polyesters, Available from Eastman Chemical Company,Kingsport, TN, USA) 5 70 wt % AQ35S White, tack- 0.5 30 wt % glycerinfree, flexible. 6 70 wt % AQ38S White, tack- 0.5 30 wt % glycerin free,flexible. 7 70 wt % AQ55S Clear, tack- 0.2 30 wt % glycerin free,flexible.

EXAMPLE 7b

Several compositions comprising 70 wt % ethylene acrylic acid copolymersin 30 wt % glycerin were prepared. Each sample was prepared by firstmixing 52 grams of ethylene acrylic acid copolymer material (a 25 wt %solids emulsion) with 5.57 grams of glycerin in a 60 milliliter glassjar. The combined materials were then mixed for 10 minutes to result inan emulsion. The resulting emulsion was then cast onto a sheet of 0.004inch thick transparency film (PP2500 series 3M transparency film) atroom temperature. The cast emulsion was then allowed to dry-down under aheat lamp to form a film. The samples were then evaluated for filmproperties and RF heating.

TABLE 7 Time to Composition Melt Experiment # Description FilmProperties (s) ETHYLENE ACRYLIC ACID COPOLYMERS (Acid Form) . . .(MICHEM 4983P, Available from Michelman Incorporated, Cincinnati, OH,USA) 1 100 wt % MICHEM Clear, colorless, 28 4983P brittle, tack-free. 270 wt % MICHEM Clear, colorless, less 0.5 4983P brittle, tack-free. 30wt % glycerin 3 50 wt % MICHEM Clear, colorless, 0.4 4983P flexible,tack-free. 50 wt % glycerin ETHYLENE ACRYLIC ACID COPOLYMERS (SodiumSalt Form) . . . (MICHEM 48525P, Available from Michelman Incorporated,Cincinnati, OH, USA) 4 100 wt % MICHEM Clear, colorless, No Heating48525P brittle, tack-free. in 1 minute. 5 70 wt % MICHEM Clear,colorless, 0.5 48525P flexible, tack-free, 30 wt % glycerin rubbery. 650 wt % MICHEM Clear, colorless, 0.2-0.4 48525P flexible, tack-free, 50wt % glycerin rubbery.

EXAMPLE 7c

Several compositions comprising 70 wt % vinyl acetate acrylic copolymersin 30 wt % glycerin were prepared. Each sample was prepared by firstmixing 46.67 grams of vinyl acetate acrylic copolymer material (a 55 wt% solids emulsion) with 3 grams of glycerin in a 60 milliliter glassjar. The combined materials were then mixed for 10 minutes to result inan emulsion. The resulting emulsion was then cast onto a sheet of 0.004inch thick transparency film (PP2500 series 3M transparency film) atroom temperature. The cast emulsion was then allowed to dry-down under aheat lamp to form a film. The samples were then evaluated for filmproperties and RF heating.

TABLE 8 VINYL ACETATE ACRYLIC COPOLYMERS . . . (ROVACE HP3442, Availablefrom Rohm and Haas, Philadelphia, PA, USA) Composition Time to MeltExperiment # Description Film properties (s) 1 100 wt % HP3442 Clear,colorless, No Melting flexible, tack-free. in 1 minute 2 90 wt % HP3442Clear, colorless, 0.3 10 wt % glycerin flexible, very tacky, with goodcohesion.

EXAMPLE 7d

This example demonstrates how the addition of glycerin as well asadjustments in pH to gelatin solutions can affect the properties ofderived gels.

Several compositions were prepared as solutions of a commerciallyavailable gelatin (Eastman 45Y56-853-3V0-6CS available from EastmanGelatine Corporation). All compositions had water. Some solutions hadglycerin added to them. Some solutions had their pH adjusted by theaddition of 10N NaOH or 6N HCl. The compositions were prepared asfollows:

Composition #1 was prepared by adding 70 grams of gelatin to 280 gramsof water and stirring and heating the resulting mixture at about 65° C.for 1 hour to obtain a solution. The solution had a pH of 6.18 at 65° C.

Composition #2 was prepared by stirring 6 grams of glycerin into 70grams of composition #1. The solution had a pH of 5.8 at 65° C.

Composition #3 was prepared by stirring drops of 10 N NaOH (about 25drops) into 125 mls of composition #1, until the resulting solution hada pH. of 10.1 at 65° C.,

Composition #4 was prepared by stirring 8.51 grams of glycerin into 99.3grams of composition #3 to result in a solution with a pH of 10.1 at 65°C.

Composition #5 was prepared by stirring drops of 6N hydrochloric acid(about 90 drops) into 125 grams of composition #1, until the resultingsolution had a pH of 1.9 at 65° C.

Composition #6 was prepared by stirring 5.361 grams of glycerin into62.57 grams of composition #5 to result in a solution with a pH of 1.9at 65° C.

Each gelatin solution was cast onto a sheet of transparency film (3MPP2500 Transparency Film) and allowed to set-up at room temperature toform a gel film. The gels differed in their film properties and in theirRF-heating properties as described in Table 9.

Gelatin films (susceptors) may not act as a good adhesive on low energysurfaces, such as PE, PP, etc. However, the are expected to performeffectively as adhesives on polar substrates, such as paper, Kraftpaper, linear boards wood, etc.

TABLE 9 GELATINS . . . (Eastman 45Y56-853-3V0-6CS gelatin, Availablefrom Eastman Gelatin, USA) Experiment Time to Melt # CompositionDescription Film properties (s) 1 gelatin Brittle w/ No Heating pH 5.8at 65° C. poor adhesion to in substrate. 1 minute. 2 70 wt % gelatinFlexible w/ 10 30 wt % glycerin good adhesion to pH 5.8 at 65° C.substrate. 3 gelatin Brittle w/ No Heating pH 10.1 at 65° C. pooradhesion to in substrate. 1 minute. 4 70 wt % gelatin flexible w/ 4 30wt % glycerin good adhesion to pH 10.1 at 65° C. substrate. 5 gelatinBrittle with poor 17 pH 1.9 at 65° C. adhesion to substrate. 6 70 wt %gelatin Flexible w/good <1 30 wt % glycerin attachment to pH 1.9 at 65°C. substrate.

EXAMPLE 8

Several compositions were prepared by mixing various polar materialswith a representative ionomer (Eastman AQ35S Sulfopolyester). In eachcase, the compositions are demonstrated to be more susceptible to RFheating than the component ionomer or polar material by themselves.

Each composition is comprised of 70 wt % AQ35S in 30 wt % polarmaterial. Each sample was prepared by first mixing 46.67 grams of AQ35D(a 30 wt % solids emulsion) with 6 grams of polar carrier in a 60milliliter glass jar. The combined materials were then mixed for 10minutes to result in an emulsion. The resulting emulsion was then castonto a sheet of 0.004 inch thick transparency film (PP2500 series 3Mtransparency film) at room temperature. The cast emulsion was thenallowed to dry-down under a heat lamp to form a film. The samples werethen evaluated for film properties and RF heating.

TABLE 10 VARIOUS POLAR MATERIALS USED IN COMPOSITIONS COMPRISING: 70 wt% EASTMAN AQ35S/30 wt % POLAR MATERIAL. Time to Experiment Film Melt #Composition Description properties (s) 1 70 wt % EASTMAN AQ35S Clear,tack- 1 30 wt % Ethylene Glycol free, (The DOW Chemical Company,flexible. Midland, MI, USA) 2 70 wt % EASTMAN AQ35S White, 0.150 30 wt %1,2-propylene glycol slightly (The DOW Chemical Company, tacky, Midland,MI, USA) flexible. 3 70 wt % EASTMAN AQ35S Clear, 0.4 30 wt %polyethylene glycol 200 yellow, (Union Carbide Chemicals and tacky,Plastics Company Inc., flexible. Danbury, CT, USA) 4 70 wt % EASTMANAQ35S Cloudy, 12 30 wt % polyethylene glycol 8000 orange, tack- (UnionCarbide Chemicals and free, w/some Plastics Company Inc., undissolvedDanbury, CT, USA) polyethylene glycol, flexible. 5 70 wt % EASTMAN AQ35SWhite, tack- 1.5 30 wt % hexylene glycol free, (Shell Chemical Company,flexible. Houston, TX, USA) 6 70 wt % EASTMAN AQ35S Clear, .25 30 wt %diethylene glycol slightly (The DOW Chemical Company, tacky, Midland,MI, USA) flexible. 7 70 wt % EASTMAN AQ35S Clear, tack- <0.5 30 wt %glycerin free, (The Procter and Gamble flexible. Company, Cincinnati,USA) 8 70 wt % EASTMAN AQ35S Slightly 2 30 wt % sorbitol cloudy, (Sigma,St. Louis, MO, USA) slightly tacky, flexible. 9 70 wt % EASTMAN AQ35SClear, 10 30 wt % NPC-ST-30, Colloidal yellow, silica in ethylene glycolslightly monopropyl ether. tacky, (Nissan Chemical Company, flexible.Japan; New York Office, Tarrytown, NY, USA) 10 70 wt % EASTMAN AQ35SSlightly 0.2 30 wt % EG-ST, Colloidal cloudy, silica in ethylene glycol.slightly (Nissan Chemical Company, tacky, Japan; New York Office,flexible. Tarrytown, NY, USA) 11 100 wt % EASTMAN AQ35S Clear, tack- NONO ADDED POLAR free, HEAT MATERIALS (CONTROL) flexible. in 1 minute. 1270 wt % EASTMAN AQ35S Clear, tack- 2.8 30 wt % N-methylpyrrolidone free,(Aldrich Chemical Co., Inc. flexible. Milwaukee, WI) 13 70 wt % EASTMANAQ35S Clear, tack- 0.3 30 wt % dimethyl formamide free, (AldrichChemical Co., Inc. flexible. Milwaukee, WI) 14 70 wt % EASTMAN AQ35SClear, 0.2 30 wt % formamide slightly (Aldrich Chemical Co., Inc. tacky,Milwaukee, WI) flexible. 15 70 wt % EASTMAN AQ35S Clear, 0.15 30 wt %dimethyl sulfoxide slightly (Aldrich Chemical Co., Inc. tacky,Milwaukee, WI) flexible.

EXAMPLE 9

Thermoset polymers are a class of polymeric systems formed by chemical(usually covalent bonding) reaction of lower molecular weight functionalbuilding blocks. For instance, epoxy thermoset polymers are formed bythe reaction of oxirane groups of epoxy compounds with other functionalgroups such as hydroxyl, carboxyl, amine etc. In the case of urethanes,isocyanate groups are reacted with functional groups such as amines,hydroxyls etc. Chemical reactions of the functional groups of thebuilding blocks typically need energy source such as heat, radiation andpresence of catalyst. The reaction product resulting from such aninteraction leads to crosslinking between the functional groups of thebuilding blocks which in turn gives a cured polymeric system with manydesirable properties such as improved heat, chemical and solventresistance, enhanced strength and mechanical properties etc. A keyfeature of thermoset systems is the fact that once the crosslinks areformed in the cured state it is very difficult to reverse it.

A convenient way to study the crosslinking reaction in a thermosetsystem is to follow the gelling reaction. At the start of thecrosslinking reaction, viscosity of the initial reaction mixture is low.In the presence of appropriate catalyst and energy source, chemicalcrosslinking starts to take place with increase in molecular weight andviscosity. After a critical stage of the crosslinking reaction has takenplace, the system sets up to an insoluble (in a solvent such as MEK inwhich the starting compounds are soluble) gel. Physico-chemically,chemical bonds are being formed leading to a network structure of thecured system. It has been shown that many of the properties of athermoset system (such as glass transition temperature, solvent andchemical resistance, mechanical properties etc.) can be readilycorrelated to the gel content of the system.

The degree of cross linking of various thermoset systems was assessed bymeasuring the gel content of formulation after exposure to RF field todifferent time and energy levels. Increase in gel content of a givencomposition after RF exposure (compared to the gel content of the samecomposition after air drying for several hours) is taken as a measure ofcure of the thermoset system.

Typical gel measurements were carried out as follows.

A sample of the formulation is applied to a glass slide. The sample isair dried for a 1-2 hours so the applied layer is dry to touch. Sampleweight is noted as “A” after taking into account the tare weight ofglass slide. Then it is exposed to RF source (in the case of controlexperiments, the sample is put in a conventional laboratory oven at aset temperature and time). The cured sample is cooled down to ambienttemperature. The glass slide containing the cured sample is dipped in 40ml of MEK for 10 minutes. The slide is taken out and air-dried prior toweighing. Sample weight is noted as B.

% Gel content is calculated as (B/A)×100

It is worth noting that gel content as measured by the above proceduregives only the initial cure state of the thermoset system. Typically,crosslinking reaction progress further upon aging leading to a highercured state of thermoset system.

In the following experiments, the following materials were used:

EPON 828: Diglycidylether of bisphenol-A from Shell Chemicals.

ANCAMINE 2441 catalyst, a modified polyamine from Air Products &Chemicals Inc.

EpiRez dispersion, a bisphenol A based epoxy dispersion from ShellChemicals.

Epicure 8536-MY60, an amine curing agent from Shell Chemicals.

MAINCOTE HYDUR, a self-reactive acrylic emulsion from Rohm & Haas.

Aropol 7241, an isophthalic polyester (unpromoted) from AshlandChemical.

KELSOL 5293, a water dispersible polyester from Reichhold.

CYMEL 385, butylated urea formaldehyde resin from Cytec Industries.

DESMODUR-W, an aliphatic diisocyanate {CAS #5142-30-1,(4-isocyanatocyclohexyl) methane} from Bayer

FORMREZ 11-36, a polyester diol from Witco

T-12 catalyst, dibutyltindilaurate from Air Products & Chemicals Inc.

Eastman A 35 D. sulfonated branched polyester from Eastman Chemicals.

A. Epoxy Resins:

Epoxy resins are typically cured to a thermoset state by application ofheat in the presence of catalysts such as amines, acids, anhydrides etc.By proper selection of epoxy resin, catalyst (amine, acid etc.) andoptionally a polar carrier such as water, glycerin and similar highdielectric constant liquids, it is possible to formulate RF curedthermoset epoxy systems of potential interest in diverse applications,such as: adhesives and coatings for conventional and spray applicationson plastics, metals, wood, etc.; corrosion resistant coatings;industrial and protective coatings; top coats; automotive coatings;lamination of composites; laminating adhesives; bonding of structuralcomposites; inks and decorative coatings; barrier coatings; etc.

The effect of time and temperature on some thermally cured epoxy resinsystems using typical cure conditions is shown in this example. Thecomposition included:

EPON 828 resin 3 parts ANCAMINE 2441 catalyst 0.3 parts

The above composition was air dried without any heat and the gel contentmeasured. It was found to be zero showing that the resin is notcross-linked to a cured system.

The above composition was heated to 130 deg C. for 5 minutes and the gelcontent of the sample was found to be 11%. This shows that there is somecrosslinking occurring under this condition.

The above composition was heated to 130 deg C. for 15 minutes and thegel content was found to be 48%. As expected, longer exposure to highertemperature increases crosslink density and gel content.

The above composition was heated to 120 deg C. for 20 minutes and thegel content was found to be 42.5%. This shows that longer exposure timeat a lower temperature compared to previous experiment did not increasegel content. From this observation, one can conclude that temperaturehas a more significant influence on crosslink density and gel content ofthe system.

The above composition was exposed to 120 deg C. for 30 minutes and thegel content was found to be 73.5%.

The main conclusion from the above experiments is that a fairly longtime (order 30 minutes) is needed to reach a high gel content thermosetepoxy resin system, cured by conventional thermal energy.

In the next series of experiments, similar epoxy compositions wereevaluated when exposed to RF (14.7 MHz) for various lengths of time andenergy. The composition included:

EPON 828 2.1 Parts ANCAMINE 2441 0.5 parts

The above composition was air-dried and the gel content of the driedsample was found to be 10.7%. This shows that there is a very smalllevel of gel in the air-dried (1 hour) sample.

10% Glycerin was added to the above composition and the sample air-driedfor 1 hour and its gel content was found to be 4.3%. This data showsthat glycerin tends to solubilize the gel under air dry condition.

The above composition (without glycerin) was applied onto a glass slideand was exposed to 500 mv for 2.5 minutes and its gel content was foundto be 8.5%. This shows that there is not much activation under thislevel of RF energy.

The 10% glycerin composition was applied to a glass slide and the samplewas exposed to 500 mV for 2.5 minutes. Gel content of the sample wasfound to be 77.3%. This result shows that addition of glycerin enhancesthe RF susceptibility of the resin and high level of crosslinking isachieved.

These experiments clearly show that epoxy resins can be activated in avery short period of time (compared to thermal curing conditions),especially in the presence of a polar carrier such as glycerin.

In the next series of experiments, another type of epoxy and curingagent was tested. The composition included:

EPI-REZ 3520-WY-55 2 parts Epicure 8536-MY60 1 parts

The above composition was applied to a glass slide and activated under100 mV for 5 minutes. No heat was noted and the gel content was found tobe 19.3%

The same composition was activated under 500 mV for 5 minutes. Gelcontent was found to be, 25.5%. This shows that higher power compared tofirst experiment is needed for crosslinking to take pace.

10% Glycerin was added to the above composition and the sample, afterdrying on a glass slide, was activated for 5 minutes under 500 mV. Thegel content was found to be 52.4%, which is very similar to what wasobtained without any glycerin. This result shows that the presence ofglycerin or other carrier is not necessary for RF activation in allcases, especially if the resin system is water based such as the Epi Rezresin.

B. Acrylic system:

In this series of experiments, the use of RF activation for an acrylicclass of resin is demonstrated.

MAINCOTE HYDUR 30, a water based acrylic emulsion with carboxyl andunsaturation functionalities from Rohm and Haas was tested. The samplewas air-dried and its gel content was found to be 37%. This result showsthat the unsaturation in the acrylic resin results in some crosslinkingdue to air oxidation, as seen in drying oils and alkyd resins.

10% glycerin was added to MAINCOTE HYDUR 30 and the gel content of theair dried sample was found to be 4.6%. This result shows that glycerinacts as good solvent for the air-dried sample.

MAINCOTE HYDUR 30 was applied to a glass slide and the sample exposed to500 mV for 2.5 minutes. The gel content was found to be 61.5%. Thisclearly shows that RF field activates the acrylic resin leading to highlevels of crosslinking.

10% Glycerin/MAINCOTE HYDUR 30 was exposed to 500 mV for 2.5 minutes.The gel content was found to be 92.3%. This result shows that presenceof glycerin promotes RF coupling with the resin.

MAINCOTE HYDUR 30 was exposed to 700 mV for 2.5 minutes and the gelcontent was found to be 81.8%. This shows that increased RF powerpromotes crosslinking of acrylic resin.

10% Glycerin/MAINCOTE HYDUR 30 was exposed to 700 mV for 2.5 minutes andthe gel content of the sample was found to be 100%. This result showsthe beneficial role of glycerin in promoting RF activation of acrylicresin.

The next experiment is a comparative example showing thermal curing ofacrylic resin. MAINCOTE HYDUR was heated to 100 deg C. for 5 minutes andthe gel content was found to be 93%. Note that gel content of RFactivated sample is higher even though it was exposed only for half theduration to energy.

This series of examples show that functionalized acrylic polymers can beactivated under RF energy.

C. Polyester Resin

In this series of experiments, the RF response of polyester/vinyl esterresins was studied.

Aropol 7241, an isophthalic polyester resin from Ashland Chemical, wasapplied to a glass slide and the dried sample was exposed to RF field at500 mV and 5 minutes. The gel content was found to be 51.3%.

This result shows that RF energy can activate an isophthalic polyesterresin.

KELSOL 5293, a polyester dispersion from Reichhold Chemicals, was testedin this example. The composition included:

KELSOL 5293 2 parts CYMEL 385 crosslinker 0.6 parts

The composition was exposed to RF for 2.5 minutes at 500 mV. The gelcontent was found to be 8.5%.

10% glycerin was added to the composition and exposed to RF for 2.5minutes at 500 mV. The gel content was found to be 21.9%. This showsthat addition of glycerin promotes RF activation.

The above composition (without glycerin) was exposed to 700 mV for 2.5minutes and the gel content was found to be 73.7%. This result showsthat exposure to higher RF field leads to higher gel content.

The composition comprising 10% glycerin was exposed to 700 mV for 2.5minutes and the gel content was found to be 59.5%.

These experiments show that RF energy can be used to activate polyestertype resins.

D. Urethanes

A linear polyurethane composition based on DESMODUR-W (an aliphaticdiisocyanate from Bayer) and FORMREZ 11-36 (a polyester diol from Witco)was evaluated. The composition included:

DESMODUR W 0.75 parts Formerez 11-36 32 parts T-12 catalyst from AirProducts & Chemicals 1-2 drops

A glass slide containing the above composition was exposed to 700 mV RFfield for 5 minutes and the gel content was measured to be 11.4%. (Note:At 500 mV, the gel content was zero for 2.5 and 5 minute exposureswithout glycerin and 1.3% and 8.3% for 2.5 and 5 minute exposures with10% glycerin)

10% Glycerin was added to the above composition and the RF activationrepeated under the same conditions (700 mV and 5 minutes). The gelcontent was found to be 27%. This level of gel content is quite good fora linear polyurethane.

This result shows that addition of glycerin promotes urethane reactionand gel formation. It is very likely that hydroxyl groups present in theglycerin molecule is acting as reactive polyol in the formation ofurethane. It may be possible to increase the gel content by increasingthe ratio of isocyanate in the formulation relative to polyol. It mayalso be possible to increase the gel content of the composition bypartially replacing the diisocyanate (DESMODUR W) and polyester diol(Formerez 11-36) with multifunctional isocyanate such as polymeric MDI(methylene bisdiphenyldisocyanate) and triols. Use of multifunctionalisocyanate and polyol should significantly increase gel content close to100%. Use of isocyanate terminated prepolymer of higher molecular weight(8,000-10,000) in the urethane reaction may also increase gel content ofthe system.

EXAMPLE 10 Effect of “Susceptor” Addition on RF Activation of Acrylicand Polyesters

The effect of adding 4-styrene sulfonic acid, Na salt, vinyl sulfonicacid, Na salt and A 35 D sulfonated polyester from Eastman Chemicals onRF activation of acrylic and polyester resins was evaluated. A firstcomposition included:

MAINCOTE HYDUR- 95 parts 4-styrene sulfonic acid, Na salt 5 parts

The above composition was evaluated as described in previous examples at700 mV and 2.5 minutes. The gel content was found to be 45.5%. Gelcontent of the sample without 4-styrene sulfonic acid, Na salt, underthe same conditions was found to be 81.8% (see above).

10% Glycerin was added to the above composition and the sample evaluatedunder 700 mV and 2.5 minutes exposure conditions. The gel content wasfound to be 66.7%. Gel content of the sample without susceptor was 100%(see above).

This result shows that styrene sulfonate, Na salt does not promote theRF activation of acrylic resin, with and without glycerin.

A second composition included:

KELSOL 5243 polyester 2 parts CYMEL 0.6 parts Vinyl sulfonic acid, Nasalt At 25% in water 0.5 parts

The above composition was evaluated as before at 700 mV and 2.5 minutes.The gel content was found to be 67.2%. Similar composition withoutsusceptor had a gel content of 73.7% (see above). This result shows thataddition of vinyl sulfonic, Na salt, does not promote RF activation ofpolyester resin.

10% Glycerin was added to the above composition. The resultantcomposition was evaluated as before under 700 mV and 1 second RF field.The sample became too hot and burst into flames. The result shows thatglycerin does activate under high field and it is possible to get highdegree of crosslinking reaction under very short times, say less than 1second.

A third composition included:

MAINCOTE HYDUR acrylic 1 part Eastman AD 35 D polyester susceptor 1 part

The above composition was evaluated as before and the gel content wasfound to be 79.2% at 700 mV and 2.6 minutes. The same compositionwithout the susceptor had a gel content of 81.8% at 700 mV and 2.5minutes exposure (see above). In this case addition of a susceptor doesnot have any effect on RF activation of acrylic polymer.

10% Glycerin was added to the third composition which was exposed to 700mV for 2 minutes. This exposure led to a very violent reaction. Thisshows that susceptor was too active.

The third composition was exposed to 500 mV for 5 minutes. Gel contentwas found to be 68.4%. A comparable sample without the addition ofsusceptor was found to give a gel content of 61.5% after 2.5 minutesexposure (see above). The result shows that the susceptor had verylittle effect.

The third composition comprising 10% glycerin in was evaluated at 500 mVand 5 minutes. The gel content was found to be 69.7%. The same samplewith out susceptor had a gel content of 92.3% at 500 mV and 2.5 minuteexposure (see above). The result shows that the addition of susceptorhad a negative effect on RF activation.

It appears addition of known susceptors to the various thermoset resincompositions has very little impact on RF activation of the resins. Insome cases, it seems to have a negative impact.

In a few cases, the heat generation is quite violent suggesting thatproper tuning of frequency/power/time and other variables will lead toconditions that would allow very short cure times.

EXAMPLE 14

The use of the carboxyl containing diol dimethylol butanoic acid wastested as a susceptor. The composition included:

Formerez 11-36 3.2 parts DESMODUR W 0.75 parts Dimethylol Butanoic acid0.28 parts T-12 catalyst 1-2 drops

No significant activation took place when this composition was exposedto 500 mV level (2.5 and 5 minute exposure). At 5 minute exposure under700 mV, the glass slide broke and no data could be gathered. As notedabove, under similar conditions without the susceptor, a gel content of11.4% was obtained in the absence of glycerin and 27% in the presence ofglycerin.

It may be useful to add the acid diol in N-methyl pyrrolidone or anotherpolar solvent and neutralize with a tertiary amine to protonate theacid. Further use of urethane prepolymer containing carboxyl orsulfonate groups in the presence of a tertiary amine (to protonate theacid) may be a better susceptor candidate for the urethane reaction.

EXAMPLE 15

This example demonstrates a method of selectively activating thecompositions of the invention within a multi-layer stack of materials.

The composition comprised 70 wt % Eastman AQ35S sulfopolyester in 30 wt% glycerin. The composition was applied and dried down from an aqueousdispersion to form a continuous 0.003 inch thick film on one side of abilaminate polyolefin material. The bilaminate polyolefin materialcomprised a single layer of polypropylene (PP) non-woven material bondedto a single layer of polyethylene (PE) film. The composition Was coatedonto the PP side of the bilaminate material. The coated bilaminatematerial was then interposed between two multi-layer stacks of un-coatedbilaminate material to form a composite sandwich of materials. Eachmulti-layer stack had two layers of the un-coated bilaminate polyolefinmaterial. The composite sandwich (410) was then placed directly over theRF probes and compressed under a TEFLON™ block at 30 psi. Thecomposition was RF heated by applying approximately 1 kW of forwardpower into the tuned heat station 4122 for 200 milliseconds atapproximately 13.5 MHz. After applying the RF energy to the compositesandwich, the pressure was removed and the sandwich was evaluated byslowly pulling the layers apart by hand. Every layer was easily pulledapart, with no observed bonding, except for the two layers that were indirect contact with the bonding composition. The two layers that were indirect contact with the bonding composition were firmly adhered by thebonding composition. As a control experiment, the experiment wasrepeated, except that no RF energy was applied to the compositesandwich. This experiment resulted in no observable bonding between anyof the layers, including the two layers that were in direct contact withthe bonding composition. It should be understood that in thisexperiment, the bonding composition was pre-applied to one surface ofone of the layers of the composite sandwich. The bonding compositioncould be applied to more than one surface of more than one layer.Bonding would occur between any layers that are each in contact with agiven layer of bonding composition.

EXAMPLE 16

This example demonstrates the method of interfacing a carrier layer ontothe surface of a susceptor layer to achieve an RF heatable composition.First, a 0.003 inch layer of a sulfonated polyester copolymer, EastmanAQ35S (Supplied by Eastman Chemical Company, Kingsport. Tenn.) wascoated out of an aqueous dispersion onto the polypropylene (PP)non-woven side of a bilaminate web consisting of a layer of PP non-wovenbonded to a layer of polyethylene (PE) film. The coating was thoroughlydried down under a heat lamp and fan. A sandwich was made by placing asample of the coated web against the PP side of a second piece of thesame web material which was not coated, such that the coating wasbetween the two webs. The sandwich was placed directly over the RFprobes (410) of the RF set-up described in FIG. 41. The distance betweenthe RF probes and the sandwich was about 0.010 inch. The sandwich layerswere pressed firmly together against the RF probes with 35 psi ofapplied pressure. About 1 kW of 13.5 MHz RF energy was applied for 500milliseconds and resulted in no noticeable heating or bonding betweenthe webs. Then the sandwich layers were separated and the susceptorcoating was moistened with distilled water. The sandwich wasre-assembled and RF energy was applied to it for 500 milliseconds asdescribed above, resulting in very good bonding of the webs. As acontrol experiment, a sandwich consisting of two webs of the un-coatedweb material was prepared by moistening the PP side of each web andbringing the water moistened surfaces together. RF energy was appliedfor 500 milliseconds to the sandwich in the same way described above,resulting in no noticeable heating.

EXAMPLE 17

This example demonstrates the effect of varying the concentration of thepolar carrier in blends of the polar carrier and an ionomer. The polarcarrier of this example is glycerin. Glycerin has a dielectric constant,e, of 42.5 at 25° C. The ionomer of this example is a commerciallyavailable sulfonated polyester ionomer (Eastman AQ55S).

Several compositions were prepared as hot-melt blends of AQ55S andglycerin. The wt. % concentration of glycerin in the compositions wasvaried from 10% to 70. The compositions were prepared as follows:

Each composition was prepared to have a total mass of 50 grams. For eachcomposition, the respective amounts of AQ55S pellets and glycerin wereinitially weighed into a resin flask and mixed to achieve thoroughwetting of the resin pellets with the glycerin. The flask was then fitwith a condenser column and sealed stir-assembly, and partially immersedinto a 335 F. hot oil bath to achieve controlled heating and melting ofthe mixture. After the pellets became molten and swollen with theglycerin, the mixture was stirred and blended into a uniformcomposition.

Each composition was then applied in its molten state as a 0.003 inchthick×1 inch wide×5 inch long, continuous layer along the center line ofa 4 inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end. The resulting coatings differed intheir relative RF-heating properties as well as their relative heatresistance to bond failure in a given shear loading condition.

RF-heating of each composition was evaluated as follows. For eachcomposition, several sandwiches were prepared. Each sandwich was made byplacing the polypropylene (PP) non-woven side of a 1 inch wide×4 inchlong strip of a bilaminate web against the coated side of the coatedacetate test strip. The bilaminate web was composed of a layer of PPnon-woven bonded to a layer of polyethylene (PE) film. Each sandwich wasplaced directly over the RF probes (410) of the RF set-up described inFIG. 41, such that the uncoated side of the acetate test strip wasplaced toward the probes. The sandwich layers were pressed firmlytogether against a layer of 0.010 inch thick layer of TEFLON™ andacetate that separated the RF probes and sandwich. A single pulse of 0.5kW, 13.5 MHz RF energy was applied for a controlled duration to eachsandwich. For each composition several sandwiches were activated, eachat an incrementally longer duration. This gave a range of RF heatingresults. Threshold RF activation was determined from each range ofresults as the minimum duration that result in sufficient melting andwetting of the adhesive coating to the web to be observed by the nakedeye. Threshold RF activation by the specific RF set-up(generallyindicated in FIG. 41) resulted in a narrow band of heating that wasbiased toward and parallel to the “high” probe of the probe assembly(602 or 604). This was because an “unbalanced” impedance matchingnetwork was used in the set-up.

Resistance to shear load bond failure was evaluated as follows. For eachcomposition, bonded specimens were prepared. The specimens eachconsisted of a sandwich of a 1 inch×4 inch×0.0035 inch thick layer ofacetate pressed against and hot-melt bonded to the coated side of acoated acetate test strip. (The coated acetate test strips were preparedas described earlier in this example.) Each hot-melt bond wasfacilitated by pressing the sandwich on a 275 F. hot plate surface undera 0.5 Kg load for 30 seconds, and then removing the sandwich andallowing it to cool and solidify into a bonded specimen. Each sandwichhad a pair of “tails” of unbonded acetate on each side of a centered 1inch×1 inch bonded area of the sandwich. One tail from each of the twopairs and on opposite sides of the sandwich was cut off. This resultedin the final bonding specimen, consisting of two 1 inch×3 inch layers of0.0035 inch thick acetate bonded together across a 1 inch by 1 inchoverlap by an interposed 0.003 inch thick layer of the composition beingtested. The specimens were then placed under a shear load of 0.5 Kg in atemperature controlled chamber at 100 F. The time required to result intotal bond failure (disassembly of the specimen) at 100 F. was measuredfor each specimen and is referred to herein as “Shear Holding Time”.

The following observations were made:

(1) As the percentage of glycerin was increased from 10% to 70%, a sharpincrease in relative rates of RF heating began to occur at about 10%glycerin. (See FIG. 54.)

(2) As the percentage of glycerin was decreased from 70% to 10% a sharpincrease in relative heat resistance began to occur at about 30%glycerin. (See FIG. 55.)

EXAMPLE 18

This example demonstrates the effect of varying the concentration of thepolar carrier in blends of the polar carrier and an alternativesulfonated polyester ionomer to the AQ55S of Example 17. The polarcarrier of this example is glycerin. Glycerin has a dielectric constantof 42.5 at 25 C. The ionomer of this example is a commercially availablesulfonated polyester: ionomer (Eastman AQ35S)

Several compositions were prepared as hot-melt blends AQ35S andglycerin. The wt. % concentration of glycerin in the compositions wasvaried from 10% to 70%.

The compositions were prepared as follows:

Each composition was prepared to have a total mass of 50 grams. For eachcomposition, the respective amounts of AQ35S pellets and glycerin wereinitially weighed into a resin flask and mixed to achieve thoroughwetting of the resin pellets with the glycerin. The flask was then fitwith a condenser column and sealed stir-assembly, and partially immersedinto a 335 F. hot oil bath to achieve controlled heating and melting ofthe mixture. After the pellets became molten and swollen with theglycerin, the mixture was stirred and blended into a uniformcomposition.

RF-heating and resistance to shear load bond failure was evaluated foreach composition as described in Example 17.

The following observations were made:

(1) As the percentage of glycerin was increased from 10% to 30%, a sharpincrease in relative rates of RF heating began to occur at about 10%glycerin. (See FIG. 56.)

(2) As the percentage of glycerin was decreased from 30% to 20% a sharpincrease in relative heat resistance began to occur at about 30%glycerin. (See FIG. 57.) These results agreed closely with the resultsof Example 17.

EXAMPLE 19

This example demonstrates the effects of dielectric constant andconcentration of various polar carriers on the ability to achievesignificantly improved RF activation times in compositions comprisingblends of ionomers and polar carriers, as compared to compositionscomprising the ionomer without sufficient presence of polar carrier.

The polar carriers and respective measured dielectric constants of thisexample are:

(1) Propylene carbonate; ∈=62.67 at 25° C.

(2) Glycerin; ∈=42.5 at 25° C.

(3) N-methyl-2-pyrrolidone; ∈=32.2 at 20° C.

(4) 1,2-propyleneglycol ∈=32 at 25° C.

(5) Polyethylene glycol 200; ∈=17.70 at 23.5° C.

(6) Benzoflex 9-88 (dipropylene glycol benzoate); ∈=12.28 at 25° C.

The ionomer of this example is a commercially available 30% solidsaqueous dispersion of sulfonated polyester ionomer (Eastman AQ35D).Several compositions were prepared as aqueous mixtures of AQ35D and eachof the polar carriers. The wt. % concentration of polar carrier in eachof the compositions was varied from 0% up to 50%, where total weight isbased on total weight of ionomer solids combined with total weight ofpolar carrier.

The compositions were prepared as follows:

Each composition was prepared to have a total mass of 50 grams. For eachcomposition, the respective amounts of AQ35D ionomer dispersion andglycerin were initially weighed into a jar and mixed for about 10minutes. The jars were sealed with tops until castings were made.

Each composition was then applied as a liquid at room temperature intocastings onto a 0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to dry down into 0.003 inch thickcoatings. The resulting coatings differed in their relative RF-heatingproperties. RF activation was evaluated as described in Example 17.

The following observations were made:

As the percentage of each polar carrier was increased from 0% to 50%, asharp increase in relative rates of RF heating began to occur at about10% glycerin (except for the composition that was prepared fromBenzoflex 9-88, which experienced a relatively slow and gradualincrease). (See FIG. 58.)

While Benzoflex 9-88 gave a compatible composition with the AQ35Spolymer, it resulted in a significantly less RF-active composition thanany of the compositions that were prepared from more polar materialswith relatively high dielectric constants. (See FIG. 58.)

EXAMPLE 20

This example demonstrates the effect of varying the concentration of amicrocrystalline wax in the composition, X % (80% AQ55S/20% Glycerin)/Y% wax. The microcrystalline wax in this example was PARICIN 220[N-(2-hydroxyethyl)-12-hydroxystearamide].

The compositions were prepared as follows:

Each composition was prepared to have a total mass of 50 grams. A 300gram batch of 80% AQ55S/20% glycerin was prepared. 240 grams of AQ55Spellets and 60 grams of glycerin were initially weighed into a resinflask and mixed to achieve thorough wetting of the resin pellets withthe glycerin. The flask was then fit with a condenser column and sealedstir-assembly; and partially immersed into a 335 F. hot oil bath toachieve controlled heating and melting of the mixture. After the pelletsbecame molten and swollen with the glycerin, the mixture was stirred andblended into a uniform composition. After a total of 4 hours of heating,the flask was removed from the hot oil bath. Several glass jars wereeach filled with 20 grams of the molten composition. Incrementallyincreasing amounts of PARICIN 220 were weighed into the hot contents ofeach jar, to result in a concentration series of X % (80% AQ55S/20%Glycerin)/Y % PARICIN 220, where Y=0, 1, 2, 3, 4, 5, 10, 15, 20, 25 and30, and X=100−Y. Each open jar was placed in an oven at 300 F. for 30minutes and allowed to become molten. The molten contents were then handstirred with wooden stir sticks for 2 minutes to form a smooth anduniform blend.

Each composition was then applied in its molten state as a 0.003 inchthick×1 inch wide×5 inch long, continuous layer along the center line ofa 4 inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end.

The resulting coatings differed in their relative RF-heating propertiesand melt viscosities.

RF-heating was evaluated for each composition as described in Example17. The Brookfield viscosity of each composition was measured at 275 F.,using an S27 spindle.

The following observations were made:

As the wt % of PARICIN 220 was increased from 0 to 10% , there was aslight increase (<5% ) in the time required to heat each composition tothe same degree as required at 0% PARICIN 220. As the wt % of PARICIN220 was increased from 10% to 30% , there was a significant increase inthe time required to heat each composition to the same degree asrequired at 0% PARICIN 220. (See FIG. 59.)

As the wt % of PARICIN 220 decreased from 10% to 0% , the melt viscosityat 275 F. increased by a factor of 6 from 6800 cP to 42000 cP.

EXAMPLE 21

This example demonstrates the effect of varying the concentration of thepolar carrier in blends of the polar carrier and an ionomer, where theionomer is the sodium salt of an ethylene acrylic acid copolymer. Thepolar carrier of this example is glycerin. Glycerin has a dielectricconstant, ∈, of 42.5 at 25° C. The ionomer of this example is acommercially available aqueous dispersion of the sodium salt of anethylene acrylic acid copolymer (MICHEM 48525P).

Several compositions were prepared as aqueous mixtures of MICHEM 48525 Pand glycerin. The wt. % concentration of glycerin in each of thecompositions was varied from 0 % up to 50% , where total weight is basedon total weight of ionomer solids combined with total weight ofglycerin.

The compositions were prepared as follows:

Each composition was prepared to have a total mass of 50 grams. For eachcomposition, the respective amounts of MICHEM 48525 P ionomer dispersionand glycerin were initially weighed into a jar and mixed for about 10minutes. The jars were sealed with tops until castings were made. Eachcomposition was then applied as a liquid at room temperature intocastings onto a 0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to dry down into 0.003 inch thickcoatings. The resulting coatings differed in their relative RF-heatingproperties. RF activation was evaluated as described in Example 17.

The following observations were made:

As the percentage of each polar carrier was increased from 0 % to 50% ,a sharp increase in relative rates of RF heating began to occur at about10% glycerin (See FIG. 61). This result agrees well with the results ofExamples 17, 18 and 19.

EXAMPLE 22

This example demonstrates the relative heat resistance to bond failurein a given shear loading condition of four separate compositions thatare composed of four different sulfonated polyesters respectively(AQ14000, AQ35S, AQ48S and AQ55S) and the same polar material in eachcase(glycerin). The polar carrier of this example is glycerin. Glycerinhas a dielectric constant, ∈, of 42.5 at 25° C. The ionomers of thisexample are commercially available sulfonated polyester ionomers(Eastman AQ14000, AQ35S, AQ48S and AQ55S).

The four compositions were prepared to have 80 wt % ionomer/20 wt %glycerin. Each composition was prepared to have a total mass of 50grams. For each composition, the respective amounts of ionomer pelletsand glycerin were initially weighed into a resin flask and mixed toachieve thorough wetting of the resin pellets with the glycerin. Theflask was then fit with a condenser column and a sealed stir-assembly,and then partially immersed into a 335 F. hot oil bath to achievecontrolled heating and melting of the mixture. After the pellets becamemolten and swollen with the glycerin, the mixture was stirred andblended into a uniform composition.

Each composition was then applied in its molten state as a 0.003 inchthick×1 inch wide×5 inch long, continuous layer along the center line ofa 4 inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end. The resulting coatings were eachevaluated for their relative RF-heating properties as well as theirrelative heat resistance to bond failure in a given shear loadingcondition, as described in Example 17.

The following observations were made for the four compositions:

80% AQ14000/20% Glycerin

Tg of AQ14000=7° C.

Threshold RF Activation Time=130 ms

Shear Holding Time=1,604 sec

80% AQ35S/20% Glycerin

Tg of AQ35S=35° C.

Threshold RF Activation Time=310 ms

Shear Holding Time=68,252 sec

80% AQ48S/20% Glycerin

Tg of AQ48S=48° C.

Threshold RF Activation Time=90 ms

Shear Holding Time=40,346 sec

80% AQ55S/20% Glycerin

Tg of AQ55S=55° C.

Threshold RF Activation Time=100 ms

Shear Holding Time=1,450,000 sec

EXAMPLE 23

This example demonstrates a hot melt composition prepared from asulfonated polyester ionomer (AQ55S) and a polar plasticizer (RIT-CIZER#8). The composition was prepared to have 80 wt % ionomer/20 wt %RIT-CIZER #8. The composition was prepared to have a total mass of 50grams. The respective amounts of ionomer pellets and glycerin wereinitially weighed into a resin flask and mixed to achieve thoroughwetting of the resin pellets with the glycerin. The flask was then fitwith a condenser column and a sealed stir-assembly, and then partiallyimmersed into a 335 F. hot oil bath to achieve controlled heating andmelting of the mixture. After the pellets became molten and swollen withthe glycerin, the mixture was stirred and blended into a uniformcomposition. The composition was then applied in its molten state as a0.016 inch thick×1 inch wide×1 inch long, continuous layer along thecenter line of a 4 inch wide×0.0035 inch thick sheet of transparencyfilm (3M PP2500 Transparency Film). The resulting coating was evaluatedfor relative RF-heating as described in Example 17.

The following observations were made for the composition:

The composition was very thick and stiff at 335° F. It was not possibleto measure the Brookfield viscosity at 275° F. At room temperature, thecomposition was clear, tough and brittle. There seemed to be very goodcompatibility between the polymer and RIT-CIZER #8. The threshold RFactivation time was measured to be approximately 4 seconds.

EXAMPLE 24

This example demonstrates a composition that comprises an ionomer-typesusceptor, a polar material and an adhesive compound. First, severaldifferent RF susceptor compositions were prepared by blending variousionomers and polar material. Then, each of the RF susceptor compositionswere blended with an adhesive compound.

Preparation of the RF-susceptor Compositions

Several different RF susceptor compositions were prepared by blendingvarious commercially available sulfonated polyester ionomers (EastmanAQ35S, AQ48S and AQ55S, AQ1045, AQ1350, AQ14000 ) with a polar material(glycerin). The RF-susceptor compositions of this example include butare not limited to:

70 wt % AQ35S/30 wt % Glycerin

70 wt % AQ48S/30 wt % Glycerin

70 wt % AQ55S/30 wt % Glycerin

70 wt % AQ1045/30 wt % Glycerin

70 wt % AQ1350/30 wt % Glycerin

70 wt % AQ14000/30 wt % Glycerin.

Each RF-susceptor composition was prepared to have a total batch mass of300 grams. For each composition, the respective amounts of ionomer andglycerin were initially weighed into a resin flask and mixed to achievethorough wetting of the resin pellets with the glycerin. The flask wasthen fit with a condenser column and sealed stir-assembly, and partiallyimmersed into a 335 F. hot oil bath to achieve controlled heating andmelting of the mixture. After the polymer became molten and swollen withthe glycerin, the mixture was stirred and blended into a uniformcomposition. The compositions that comprised linear polymers (AQ35S,AQ48S and AQ55S) were each blended at 335 F. for 3 hours. Thecomposition comprising AQ1045 was blended at 335 F. for 1 hour. Thecompositions comprising AQ1350 and 14000 were each blended at 335 F. for1.5 hours. Each of the RF-susceptor compositions was cooled and storedat room temperature for later use.

Preparation of the Compositions Comprising Blends of RF-susceptorCompositions and an Adhesive Compound

Each of the RF susceptor compositions was blended with an adhesivecompound. The adhesive compound of this example is a random copolymer ofethylene vinyl acetate,(EVA). The commercially available EVA that wasused is DuPont Polymer's ELVAX 210, Lot #90204492.

Each composition was prepared to have a total mass of 17 grams. For eachcomposition, 7 grams of ELVAX 210 and 10 grams of the respectiveRF-susceptor composition was added to a glass jar at room temperature.The open jar was then heated in a convection oven at 335 F. for 40minutes. After 40 minutes of heating, the jar was removed from the ovento the surface of a 330 F. hot plate and stirred by hand for 1 minute toresult in a uniform smooth blend.

A total of six compositions were prepared. The RF-susceptor/Adhesivecompositions of this example include but are not limited to:

A. 41 wt % AQ35S/18 wt % Glycerin/41 wt % ELVAX 210

B. 41 wt % AQ48S/18 wt % Glycerin/41 wt % ELVAX 210

C. 41 wt % AQ55S/18 wt % Glycerin/41 wt % ELVAX 210

D. 41 wt % AQ1045/18 wt % Glycerin/41 wt % ELVAX 210

E. 41 wt % AQ1350/18 wt % Glycerin/41 wt % ELVAX 210

F. 41 wt % AQ14000/18 wt % Glycerin/41 wt % ELVAX 210

Evaluation of the Blends of RF-susceptor Compositions with ELVAX 210

Immediately after stirring the composition into a uniform blend, eachcomposition was then applied in its molten state as a 0.003 inch thick×1inch wide×5 inch long, continuous layer along the center line of a 4inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end.

The resulting coatings were each evaluated for their relative coatproperties as well RF-heating properties, as described in Example 17.

The following observations were made for the six compositions:

TABLE 11 Coating Properties RF Compo- Activation sition ToughnessClarity Color Tackiness Time (ms) A Soft Translucent White Slight Tack520 B Tough Translucent White Tacky 100 C Very Tough Translucent WhiteVery Slight 280 Tack D Very Soft Clear None Tacky 430 E Soft Clear NoneTacky 380 F Soft Clear None Tacky 340

EXAMPLE 25

This example demonstrates compositions comprising an ionomer, a polarmaterial and various low molecular weight polyolefin additives.

First, an RF heatable hot melt composition was prepared by blending 70wt % AQ35 (a sulfonated polyester, commercially available from EastmanChemical Company) with 30 wt % glycerin for about 3 hours at 335 F.Then, several compositions were prepared by blending small samples ofthe molten AQ35/glycerin blend, separately with various grades ofEPOLENE (low molecular weight polyolefins, commercially available fromEastman Chemical Company).

The polyolefin polymers of this example are Eastman Chemical's: EPOLENEN-10 (lot #11478), EPOLENE N-11 (lot #89352), EPOLENE N-14 (lot #12877),EPOLENE N-15 (lot #491104), EPOLENE N-20 (lot #87023), EPOLENE N-21 (lot#13018), and. EPOLENE N-34 (lot #12710). EPOLENE polymers are lowmolecular-weight polyolefins that can be useful as base polymers forhot-melt adhesives.

Each composition was then applied in its molten state as a 0.003 inchthick×1 inch wide×5 inch long, continuous layer along the center line ofa 4 inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end.

The resulting coatings were each evaluated for their relative RF-heatingproperties as well as their relative heat resistance to bond failure ina given shear loading condition, as described in Example 17.

Table 12 summarizes the observations that were made for the variouscompositions:

TABLE 12 mw viscosity rftime hangtime 70% AQ35/30% Glycerin + 5% EPOLENEEPOLENE# N-10 10000  8675 210 3.91 N-11  6000  7450 210 2.99 N-14  4000 7750 220 4.77 N-15 12000 13500 210 2.60 N-20 15000 10020 220 6.01 N-21 6500  6125 210 1.91 N-34  6200  8100 210 2.95 70% AQ35/30% Glycerin +10% EPOLENE EPOLENE# N-10 10000 10220 250 3.30 N-11  6000  7975 240 1.94N-14  4000  8725 250 3.33 N-15 12000 17900 250 1.46 N-20 15000  9450 2402.28 N-21  6500  7112 240 1.59 N-34  6200  8212 240 1.78 70% AQ35/30%Glycerin + X % EPOLENE N-10 % EPOLENE 0  6362 200 4.46 2.5  8337 2102.10 5  8675 210 3.91 10 10220 250 3.30 15 11570 280 5.03 20 12250 2805.99 25 14620 300 7.55 30 15250 825 5.35

EXAMPLE 26

This example demonstrates a series of compositions that comprise: 9%polyethylene glycol and 91% (75% AQ55/25% glycerin).

First, a blend of 75% AQ55 and 25% glycerin was made by blending AQ55and glycerin for 3 hours at 335 F. Then, a series of compositions wasprepared in which each composition was prepared as a molten blend of 9%polyethylene glycol (PEG) and 91% (75% AQ55/25% glycerin).

Each composition was then applied in its molten state as a 0.003 inchthick×1 inch wide×5 inch long, continuous layer along the center line ofa 4 inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end. The resulting coatings were eachevaluated for their relative RF-heating properties as well as theirrelative heat resistance to bond failure in a given shear loadingcondition, as described in Example 17.

Table 13 summarizes the observations that were made for the variouscompositions:

TABLE 13 Rftime hangtime time hrs for 1 sq. PEG # Brookfield tackrequired inch bond (PEG200 Viscosity 1 = very slight tack to melt areato fail at through (cP at 2 = slight tack sample 100 F. under a PEG8000)275 F.) 3 = tacky (ms). 0.5 kg shear load. 200 15650 1 130 12.94 30012500 1 150 11.35 400 14600 1 130 5.34 600 13700 3 140 7.23 900 12250 1150 5.76 1000  12800 1 150 6.82 1450  11700 1 210 4.85 3350  15070 1 2005.70 4000  14620 2 250 5.51 4600  16400 2 220 9.34 8000  17320 1 2306.35

EXAMPLE 27

This example demonstrates a composition comprising 10% IGEPAL. (acommercially available additive from Rhodia) and 90% (75% AQ55/25% .glycerin).

A first composition comprising 75% AQ55 and 25% glycerin was prepared byblending AQ55 and glycerin for 6 hours at 335 F. A second compositionwas prepared by blending IGEPAL CO-880 at 10 wt % with a sample of thefirst composition.

Each composition was then applied in its molten state as a 0.003 inchthick×1 inch wide×5 inch long, continuous layer along the center line ofa 4 inch wide×0.0035 inch thick sheet of transparency film (3M PP2500Transparency Film) and allowed to set-up at room temperature. Severalsuch draw downs were made for each composition. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film, each witha 1 inch×1 inch×0.003 inch thick coating of composition in the centerand 1½ inch long tails on each end.

The resulting coatings were each evaluated for their relative RF-heatingproperties as well as their relative heat resistance to bond failure ina given shear loading condition, as described in Example 17.

Table 14 summarizes the observations that were made for the variouscompositions:

TABLE 14 RF Activation Time Viscosity Time required to melt Composition(cP at 275 F.) the sample (ms). 75% AQ55/25% glycerin 28,200 180 90%(AQ55/glycerin)/  9,750 360 10% IGEPAL CO-880

EXAMPLE 28

This example demonstrates an RF heatable composition comprising 75% AQ48(a commercially available sulfonated polyester from Eastman ChemicalCompany) and 25% glycerin.

The composition was prepared by blending 75 wt % AQ48 with 25 wt %glycerin for 4 hours at 335 F. The resulting molten composition wasfluid and clear. When this composition was cast onto layers of acetateand allowed to cool, the resulting solid draw-downs were clear and hadcold-tack. This composition is ideal for Applications where parts are tobe initially adhered with a green strength bond by the composition andsubsequently fused by the heat that is generated from within thecomposition as it is exposed to RF energy.

The molten composition had a Brookfield viscosity of 5,750 cP at 275 F.,using an S27 spindle at 20 RPM. The composition was then applied in itsmolten state as a 0.003 inch thick×1 inch wide×5 inch long, continuouslayer along the center line of a 4 inch wide×0.0035 inch thick sheet oftransparency film (3M PP2500 Transparency Film) and allowed to set-up atroom temperature. Several such draw downs were made. A twin blade samplecutter was used to cut strips from the draw downs, by cutting across andperpendicular to the 5 inch long center line of each of the draw downs.This produced 1 inch wide×4 inch long strips of acetate film each with a1 inch×1 inch×0.003 inch thick coating of composition in the center and1½ inch long tails on each end. The resulting coatings were eachevaluated for their RF-heating properties, as described in Example 17.RF activation was achieved in 160 ms.

The composition was then drawn into flat beads (0.10 inches wide by 0.01inches thick at the maximum thickness—the beads were crowned in themiddle and feathered at the edges). Three sandwiches of materials weremade. Each sample was made by placing a single bead of the compositionbetween two identical layers of thin-film bilaminate polyolefinmaterial. Each layer of bilaminate material was composed of twolayers—one layer of polypropylene non-woven (PP) and one layer ofpolyethylene film (PE).

The first sandwich (sample 1 ) was assembled such that the bead was indirect contact with the PP side of one of the layers of bilaminate, andthe PP side of the other layer of bilaminate. The second sandwich(sample 2) was assembled such that the bead was in direct contact withthe PP side of one of the layers of bilaminate, and the PE side of theother layer of bilaminate. The third sandwich (sample 3) was assembledsuch that the bead was in direct contact with the PE side of one of thelayers of bilaminate, and the PE side of the other layer of bilaminate.

In each case, the bead had slight tack and was able to gently hold thelayers of the sandwich together. Each sandwich was then activated in a13.5 MHz RF field for 200 ms at 1000 watts. In each case, melting of thebilaminate layers had occurred. Then the sandwiches were each immersedand washed in MEK for several minutes in order to remove the adhesivefrom the bond line. In each case, after washing the adhesive from thesandwich, residual bonding was observed between all layers of thesandwich in the areas where melting had been observed.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents. Additionally, all patents,patent applications and publications mentioned above are incorporated byreference herein.

What is claimed is:
 1. An apparatus for heating a composition usingradio frequency (RF) energy, comprising: a direct current (DC) voltagesource; an RF amplifier coupled to the DC voltage source, wherein the DCvoltage source provides DC voltage to the RF amplifier; an impedancematching circuit coupled to an output of the RF amplifier; a firstelongated electrode connected to a first node within said impedancematching circuit; a second elongated electrode connected to a secondnode within said impedance matching circuit; and signal generatingmeans, coupled to the RF amplifier, for generating an RF signal, whereina first portion of the first electrode and a first portion of the secondelectrode are adjacent to and substantially parallel with each other, asecond portion of the first electrode is angled in a direction away fromthe second electrode, said second portion of the first electrode beingbetween said first portion and an end of the first electrode, a secondportion of the second electrode is angled in a direction away from thefirst electrode, said second portion of the second electrode beingbetween said first portion and an end of the second electrode, and whenthe RF amplifier amplifies the generated RF signal and the amplified RFsignal is provided to the impedance matching circuit, a strayelectromagnetic field is generated in a region above the space betweensaid first portion of the first electrode and said first portion of thesecond electrode, whereby the generated stray field can be used to heatthe composition when the composition is placed in said region.
 2. Theapparatus of claim 1, wherein the frequency of the RF signal is greaterthan 10 MHz.
 3. The apparatus of claim 1, wherein the power of theamplified signal is between about 50 watts and 5 kilowatts.
 4. Theapparatus of claim 1, wherein a DC voltage provided to the RF amplifierby the DC voltage source is between about 50 and 200 dc volts.
 5. Theapparatus of claim 1, wherein the impedance matching circuit comprises:a connector for receiving an RF signal; a balun transformer coupled tothe connector; a first and a second variable capacitor coupled to thebalun transformer; and an inductor connected between the first andsecond variable capacitor.
 6. The apparatus of claim 1, wherein the RFamplifier comprises means for amplifying a milliwatt signal up to amultiple kilowatt continuous wave amplitude signal with greater thaneighty percent power conversion efficiency while operating directly froma 100 to 200 VDC power source, with an instantaneous bandwidth oftwo-thirds of an octave in the middle High Frequency RF spectrum between3 and 30 MHz.
 7. The apparatus of claim 1, further comprising aprocessor for controlling the frequency of the RF signal generated bythe signal generating means, and a power sensor coupled to the impedancematching circuit for providing a signal to the processor, wherein thesignal is used by the processor in controlling the frequency of the RFsignal generated by the signal generating means.
 8. The apparatus ofclaim 7, wherein the signal provided to the processor corresponds to theamount of power reflected from the impedance matching circuit.
 9. Theapparatus of claim 7, wherein the signal provided to the processorcorresponds to the amount of power provided to the impedance matchingcircuit.
 10. The apparatus of claim 7, wherein the signal provided tothe processor corresponds to the ratio of the amount of power providedto the impedance matching circuit and the amount of power reflected fromthe impedance matching circuit.
 11. The apparatus of claim 1, whereinthe first electrode is a conductive tube.
 12. The apparatus of claim 11,wherein the first electrode has a diameter or width between aboutone-eighth of an inch and one-half of an inch.
 13. The apparatus ofclaim 1, wherein the impedance matching circuit comprises an inductor,and wherein the first electrode, the second electrode, and the inductorare connected in series such that the inductor is connected between thefirst electrode and the second electrode.
 14. A radio frequency (RF)heating system, comprising: a radio frequency (RF) amplifier; a signalgenerator that produces a radio frequency (RF) signal, said RF signalbeing amplified by said RF amplifier; an impedance matching circuitcoupled to an output of said RF amplifier; a first elongated electrodeconnected to a first node within said impedance matching circuit; and asecond elongated electrode connected to a second node within saidimpedance matching circuit, wherein a portion of the first electrode anda portion of the second electrode are adjacent to and substantiallyparallel with each other, an end of the first electrode is curled, anend of the second electrode is curled, and a stray electromagnetic fieldis generated in a region above the space between said portion of thefirst electrode and said portion of the second electrode when said RFamplifier outputs an RF signal, whereby the generated stray field can beused to heat a material that is placed in said region.
 15. The RFheating system of claim 14, wherein the impedance matching circuitcomprises: a balun transformer; a first and a second variable capacitorcoupled to the balun transformer; and an inductor connected between thefirst and second variable capacitor.
 16. The RF heating system of claim14, further comprising a processor for controlling the frequency of theRF signal generated by the signal generator, and a power sensor coupledto the impedance matching circuit for providing a signal to theprocessor, wherein the signal is used by the processor in controllingthe frequency of the RF signal generated by the signal generator. 17.The RF heating system of claim 16, wherein the signal provided to theprocessor corresponds to the amount of power reflected from theimpedance matching circuit.
 18. The RF heating system of claim 16,wherein the signal provided to the processor corresponds to the amountof power provided to the impedance matching circuit.
 19. The RF heatingsystem of claim 16, wherein the signal provided to the processorcorresponds to the ratio of the amount of power provided to theimpedance matching circuit and the amount of power reflected from theimpedance matching circuit.
 20. The RF heating system of claim 14,wherein the first electrode has a diameter or width between aboutone-eighth of an inch and one-half of an inch.
 21. The RF heating systemof claim 14, wherein the impedance matching circuit comprises aninductor, and wherein the first electrode, the second electrode, and theinductor are connected in series such that the inductor is connectedbetween the first electrode and the second electrode.
 22. The RF heatingsystem of claim 14, further comprising a layer of low dielectricmaterial, said layer covering the first and second electrode so thatwhen the composition is placed in said region the layer is between theelectrodes and the composition.
 23. The RF heating system of claim 22,wherein said layer consists essentially of polytetrafluoroethylene. 24.The RF heating system of claim 14, wherein the shortest distance fromsaid portion of the first electrode to said portion of the secondelectrode is less than about 3 inches.
 25. The RF heating system ofclaim 14, wherein the shortest distance from said portion of the firstelectrode to said portion of the second electrode is less than about 1inch.
 26. A radio frequency (RF) heating system, comprising: a radiofrequency (RF) amplifier; a signal generator that produces a radiofrequency (RF) signal, said RF signal being amplified by said RFamplifier; an impedance matching circuit coupled to an output of said RFamplifier; a first elongated electrode connected to a first node withinsaid impedance matching circuit; a second elongated electrode connectedto a second node within said impedance matching circuit; and a materialhaving a low dielectric constant, wherein a portion of the firstelectrode and a portion of the second electrode are adjacent to andsubstantially parallel with each other, said material covers a topsurface of said portion of the first electrode and said portion of thesecond electrode, and a stray electromagnetic field is generated in aregion that is above the material and above the space between saidportion of the first electrode and said portion of the second electrodewhen said RF amplifier outputs an RF signal, whereby the generated strayfield can be used to heat a material that is placed in said region. 27.The RF heating system of claim 26, wherein an end of the first electrodeis curled, and an end of the second electrode is curled.
 28. The RFheating system of claim 26, wherein a second portion of the firstelectrode is angled in a direction away from the second electrode, saidsecond portion of the first electrode being between the first portionand an end of the first electrode.
 29. The RF heating system of claim26, further comprising a processor for controlling the frequency of theRF signal generated by the signal generator, and a power sensor coupledto the impedance matching circuit for providing a signal to theprocessor, wherein the signal is used by the processor in controllingthe frequency of the RF signal generated by the signal generator. 30.The RF heating system of claim 29, wherein the signal provided to theprocessor corresponds to the amount of power reflected from theimpedance matching circuit.
 31. The RF heating system of claim 29,wherein the signal provided to the processor corresponds to the amountof power provided to the impedance matching circuit.
 32. The RF heatingsystem of claim 29, wherein the signal provided to the processorcorresponds to the ratio of the amount of power provided to theimpedance matching circuit and the amount of power reflected from theimpedance matching circuit.
 33. The RF heating system of claim 26,wherein the first electrode has a diameter or width between aboutone-eighth of an inch and one-half of an inch.
 34. The RF heating systemof claim 26, wherein the impedance matching circuit comprises aninductor, and wherein the first electrode, the second electrode, and theinductor are connected in series such that the inductor is connectedbetween the first electrode and the second electrode.
 35. The RF heatingsystem of claim 36, wherein the shortest distance from said portion ofthe first electrode to said portion of the second electrode is less thanabout 3 inches.
 36. The RF heating system of claim 36, wherein saidmaterial consists essentially of polytetrafluoroethylene.
 37. A radiofrequency (RF) heating system, comprising: a radio frequency (RF)amplifier; a signal generator that produces a radio frequency (RF)signal, said RF signal being amplified by said RF amplifier; animpedance matching circuit coupled to an output of said RF amplifier; afirst elongated electrode connected to a first node within saidimpedance matching circuit; and a second elongated electrode connectedto a second node within said impedance matching circuit, wherein aportion of the first electrode and a portion of the second electrode areadjacent to and substantially parallel with each other, the firstelectrode and the second electrode are housed in a block madesubstantially from a dielectric material, and a stray electromagneticfield is generated in a region adjacent to the block and above the spacebetween said portion of the first electrode and said portion of thesecond electrode when said RF amplifier outputs an RF signal, wherebythe generated stray field can be used to heat a material that is placedin said region.
 38. The RF heating system of claim 37, wherein an end ofthe first electrode is curled, and an end of the second electrode iscurled.
 39. The RF heating system of claim 37, wherein a second portionof the first electrode is angled in a direction away from the secondelectrode, said second portion of the first electrode being between thefirst portion and an end of the first electrode.
 40. The RF heatingsystem of claim 37, further comprising a processor for controlling thefrequency of the RF signal generated by the signal generator, and apower sensor coupled to the impedance matching circuit for providing asignal to the processor, wherein the signal is used by the processor incontrolling the frequency of the RF signal generated by the signalgenerator.
 41. The RF heating system of claim 40, wherein the signalprovided to the processor corresponds to the amount of power reflectedfrom the impedance matching circuit.
 42. The RF heating system of claim40, wherein the signal provided to the processor corresponds to theamount of power provided to the impedance matching circuit.
 43. The RFheating system of claim 40, wherein the signal provided to the processorcorresponds to the ratio of the amount of power provided to theimpedance matching circuit and the amount of power reflected from theimpedance matching circuit.
 44. The RF heating system of claim 37,wherein the first electrode has a diameter or width between aboutone-eighth of an inch and one-half of an inch.
 45. The RF heating systemof claim 37, wherein the impedance matching circuit comprises aninductor, and wherein the first electrode, the second electrode, and theinductor are connected in series such that the inductor is connectedbetween the first electrode and the second electrode.
 46. The RF heatingsystem of claim 37, wherein the shortest distance from said portion ofthe first electrode to said portion of the second electrode is less thanabout 3 inches.
 47. The RF heating system of claim 37, wherein saidblock consists essentially of polytetrafluoroethylene.
 48. A radiofrequency (RF) heating system for heating a material, comprising: acircuit, wherein the circuit has a resonant frequency that changes whilethe material is being heated; a signal generator that generates an RFsignal; an amplifier coupled between the circuit and the signalgenerator that amplifies the RF signal, wherein the amplified RF signalis provided to the circuit; a reflected power sensor that senses thepower that is reflected from the circuit; and a processor coupled to thereflected power sensor and the signal generator, wherein the processorreceives from the reflected power sensor a signal that corresponds tothe power reflected from the circuit, and the processor uses said signalin controlling the signal generator so that the frequency of the signalgenerated by the signal generator tracks the resonant frequency of thecircuit while the material is being heated, wherein the circuitcomprises: an impedance matching circuit; a first elongated electrodeconnected to a first node within said impedance matching circuit; and asecond elongated electrode connected to a second node within saidimpedance matching circuit, wherein a portion of the first electrode anda portion of the second electrode are adjacent to and substantiallyparallel with each other, and a stray electromagnetic field is generatedin a region above the space between said portion of the first electrodeand said portion of the second electrode when the amplified RF signal isprovided to the circuit, whereby the generated stray field can be usedto heat the material when the material is placed in said region.
 49. TheRF heating system of claim 48, wherein an end of the first electrode iscurled, and an end of the second electrode is curled.
 50. The RF heatingsystem of claim 48, wherein a second portion of the first electrode isangled in a direction away from the second electrode, said secondportion of the first electrode being between the first portion and anend of the first electrode.
 51. The RF heating system of claim 50,wherein the shortest distance from said portion of the first electrodeto said portion of the second electrode is less than about 3 inches. 52.The RF heating system of claim 48, wherein the first electrode has adiameter or width between about one-eighth of an inch and one-half of aninch.
 53. The RF heating system of claim 48, wherein the impedancematching circuit comprises an inductor, and wherein the first electrode,the second electrode, and the inductor are connected in series such thatthe inductor is connected between the first electrode and the secondelectrode.
 54. The RF heating system of claim 48, further comprising alayer of low dielectric material, said layer covering the first andsecond electrode so that when the material is placed in said region thelayer is between the electrodes and the composition.
 55. The apparatusof claim 54, wherein said layer consists essentially ofpolytetrafluoroethylene.
 56. The apparatus of claim 48, furthercomprising a layer of low dielectric material, said layer covering thefirst and second electrode so that when the composition is placed insaid region the layer is between the electrodes and the composition. 57.The apparatus of claim 56, wherein said layer consists essentially ofpolytetrafluoroethylene.